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Pre-experimental designs.

Pre-experiments are the simplest form of research design. In a pre-experiment either a single group or multiple groups are observed subsequent to some agent or treatment presumed to cause change.

Types of Pre-Experimental Design

One-shot case study design, one-group pretest-posttest design, static-group comparison.

A single group is studied at a single point in time after some treatment that is presumed to have caused change. The carefully studied single instance is compared to general expectations of what the case would have looked like had the treatment not occurred and to other events casually observed. No control or comparison group is employed.

A single case is observed at two time points, one before the treatment and one after the treatment. Changes in the outcome of interest are presumed to be the result of the intervention or treatment. No control or comparison group is employed.

A group that has experienced some treatment is compared with one that has not. Observed differences between the two groups are assumed to be a result of the treatment.

Validity of Results

An important drawback of pre-experimental designs is that they are subject to numerous threats to their  validity . Consequently, it is often difficult or impossible to dismiss rival hypotheses or explanations. Therefore, researchers must exercise extreme caution in interpreting and generalizing the results from pre-experimental studies.

One reason that it is often difficult to assess the validity of studies that employ a pre-experimental design is that they often do not include any control or comparison group. Without something to compare it to, it is difficult to assess the significance of an observed change in the case. The change could be the result of historical changes unrelated to the treatment, the maturation of the subject, or an artifact of the testing.

Even when pre-experimental designs identify a comparison group, it is still difficult to dismiss rival hypotheses for the observed change. This is because there is no formal way to determine whether the two groups would have been the same if it had not been for the treatment. If the treatment group and the comparison group differ after the treatment, this might be a reflection of differences in the initial recruitment to the groups or differential mortality in the experiment.

Advantages and Disadvantages

As exploratory approaches, pre-experiments can be a cost-effective way to discern whether a potential explanation is worthy of further investigation.

Disadvantages

Pre-experiments offer few advantages since it is often difficult or impossible to rule out alternative explanations. The nearly insurmountable threats to their validity are clearly the most important disadvantage of pre-experimental research designs.

One-Group Posttest Only Design: An Introduction

The one-group posttest-only design (a.k.a. one-shot case study ) is a type of quasi-experiment in which the outcome of interest is measured only once after exposing a non-random group of participants to a certain intervention.

The objective is to evaluate the effect of that intervention which can be:

• A training program
• A policy change
• A medical treatment, etc.

As in other quasi-experiments, the group of participants who receive the intervention is selected in a non-random way (for example according to their choosing or that of the researcher).

The one-group posttest-only design is especially characterized by having:

• No control group
• No measurements before the intervention

It is the simplest and weakest of the quasi-experimental designs in terms of level of evidence as the measured outcome cannot be compared to a measurement before the intervention nor to a control group.

So the outcome will be compared to what we assume will happen if the intervention was not implemented. This is generally based on expert knowledge and speculation.

Next we will discuss cases where this design can be useful and its limitations in the study of a causal relationship between the intervention and the outcome.

Advantages and Limitations of the one-group posttest-only design

Advantages of the one-group posttest-only design, 1. advantages related to the non-random selection of participants:.

• Ethical considerations: Random selection of participants is considered unethical when the intervention is believed to be harmful (for example exposing people to smoking or dangerous chemicals) or on the contrary when it is believed to be so beneficial that it would be malevolent not to offer it to all participants (for example a groundbreaking treatment or medical operation).
• Difficulty to adequately randomize subjects and locations: In some cases where the intervention acts on a group of people at a given location, it becomes infeasible to adequately randomize subjects (ex. an intervention that reduces pollution in a given area).

2. Advantages related to the simplicity of this design:

• Feasible with fewer resources than most designs: The one-group posttest-only design is especially useful when the intervention must be quickly introduced and we do not have enough time to take pre-intervention measurements. Other designs may also require a larger sample size or a higher cost to account for the follow-up of a control group.
• No temporality issue: Since the outcome is measured after the intervention, we can be certain that it occurred after it, which is important for inferring a causal relationship between the two.

Limitations of the one-group posttest-only design

1. selection bias:.

Because participants were not chosen at random, it is certainly possible that those who volunteered are not representative of the population of interest on which we intend to draw our conclusions.

2. Limitation due to maturation:

Because we don’t have a control group nor a pre-intervention measurement of the variable of interest, the post-intervention measurement will be compared to what we believe or assume would happen was there no intervention at all.

The problem is when the outcome of interest has a natural fluctuation pattern (maturation effect) that we don’t know about.

So since certain factors are essentially hard to predict and since 1 measurement is certainly not enough to understand the natural pattern of an outcome, therefore with the one-group posttest-only design, we can hardly infer any causal relationship between intervention and outcome.

3. Limitation due to history:

The idea here is that we may have a historical event, which may also influence the outcome, occurring at the same time as the intervention.

The problem is that this event can now be an alternative explanation of the observed outcome. The only way out of this is if the effect of this event on the outcome is well-known and documented in order to account for it in our data analysis.

This is why most of the time we prefer other designs that include a control group (made of people who were exposed to the historical event but not to the intervention) as it provides us with a reference to compare to.

Example of a study that used the one-group posttest-only design

In 2018, Tsai et al. designed an exercise program for older adults based on traditional Chinese medicine ideas, and wanted to test its feasibility, safety and helpfulness.

So they conducted a one-group posttest-only study as a pilot test with 31 older adult volunteers. Then they evaluated these participants (using open-ended questions) after receiving the intervention (the exercise program).

The study concluded that the program was safe, helpful and suitable for older adults.

What can we learn from this example?

1. work within the design limitations:.

Notice that the outcome measured was the feasibility of the program and not its health effects on older adults.

The purpose of the study was to design an exercise program based on the participants’ feedback. So a pilot one-group posttest-only study was enough to do so.

For studying the health effects of this program on older adults a randomized controlled trial will certainly be necessary.

2. Be careful with generalization when working with non-randomly selected participants:

For instance, participants who volunteered to be in this study were all physically active older adults who exercise regularly.

Therefore, the study results may not generalize to all the elderly population.

• Shadish WR, Cook TD, Campbell DT. Experimental and Quasi-Experimental Designs for Generalized Causal Inference . 2nd Edition. Cengage Learning; 2001.
• Campbell DT, Stanley J. Experimental and Quasi-Experimental Designs for Research . 1st Edition. Cengage Learning; 1963.

Further reading

• Understand Quasi-Experimental Design Through an Example
• Experimental vs Quasi-Experimental Design
• Static-Group Comparison Design
• One-Group Pretest-Posttest Design

Causal Marketing Research

• Learning Outcomes
• Overview of Causal Research
• Three Levels of Causation
• Internal and External Validity
• Extraneous Variables
• Causal or Experimental Research Designs
• Pre-Experimental Designs
• True Experimental Designs
• Quasi-Experimental Designs
• Statistical Designs
• Laboratory and Field Marketing Research Experiments
• Test Markets
• Test Market Considerations
• Limitations of Causal Research
•   Module 1  
• |   Module 2  
• |   Module 3  
• |   Module 4  
• |   Module 5  
• |   Module 6  
• |   Module 7  
• |   Module 8  
• |   Module 9  

With an experimental research design, the researcher lays out how he or she will manipulate one of more independent variables and measure their effect on the dependent variable. Some research designs involve no manipulation of independent variables. These non-experimental designs are called ex post facto , or after the effect, studies.

An experimental design must deal with four issues:

• The people who participate in the experiment.
• The independent variable or variables, which are also called the treatment variables. These are the variables the researchers manipulate during the experiment.
• The dependent variable, or the effect that the researchers measure.
• The plan for controlling extraneous variables.

Types of Experimental Research Designs

Experimental research designs can be classified into the following typology:

Pre-Experimental Designs are the simplest form of experimental research designs. Pre-experimental designs have little or no control over extraneous variables. And, these designs do not randomly assign subjects to different treatments. As a consequence, the results of a test using a pre-experimental design are difficult to interpret. These designs are often used in testing television commercials because they are simple and relatively inexpensive.

There are three types of pre-experimental designs: One-Shot Case Studies, One Group Pre-Test - Post-Test, and Static Group tests

A.   One-Shot Case Studies: With a one-shot case study, test units—people, test markets, etc.—are exposed to a treatment. The standard notion for a treatment is the symbol "X." A single measurement of the dependent variable is taken (O 1 ). There is no random assignment of test subjects as there is only one treatment, and there is no control. Here is the standard notation for a One-Shot Case Study:

This research design has two significant flaws: 1) there is no pre-test and 2) there is no control group. A control group would, in this case, be a group that did not receive the treatment. Without these restraints, this research design cannot establish internal or external validity.

Despite these limitations, market researchers often use this design for testing new-to-the-market products.

B.   One Group Pre-Test - Post-Test: With this research design the test unit is measured twice, one before the test and once after the test. There is still no control group; which is to say, a group not receiving the treatment. Here is the standard notation for a one-group pre-test - post-test study:

Marketing researchers often use this design to test changes in the marketing plan for established products. Compared to One-Shot Case Studies, this design has the advantage of taking two measurements: one before and the other after exposure to the treatment. This allows the researcher to estimate the treatment effect by subtracting the pre-test measure from the post-test measure. But, given the lack of a control, the validity of the conclusions are questionable. Extraneous variables like history can affect the results because the observed changes in the dependent variable might be due to factors outside the research design. And, maturation can also be a problem as the observed changes to the dependent variable might be due to changes in the test subjects that are not related to the treatment. 

C. Static Group Design: With the Static Group design there is a Control Group (CG) in addition to the Experimental Group (EG). The experimental group is exposed to the treatment while the control group is not. Test units, however, are not randomly assigned to the control or experimental groups. Here is the standard notation for a Static Group study:

Measurements for both groups are made after the treatment is administered to the experimental group. The treatment effect is measured as O 1 - O 2 .

Weaknesses of this research design stem from the fact that test units are not randomly assigned to the experimental or control groups and there are no pre-test measurements taken.

True Experimental Designs are where the market researchers assign test units to treatments at random. There are three basic types of True Experimental Designs: Post-Test Only Control Group Design, Pre-Test Post-Test Control Group Design, and Solomon Four Group Design.

A. Post-Test Only Control Group Design:

With this research design, test units are randomly assigned to the experimental and control groups. The experimental group is exposed to the treatment and then both the experimental and control groups are measured. But, there is only one measurement is taken.

Here is the standard notation for a Post-Test Only study:

The effect of the treatment is calculated as O 1 - O 2 .

The advantage of this research design is that the random assignment of the test units should produce roughly equal control and experimental groups before the treatment is administered. And, the mortality for the control and experimental groups should be similar.

B. Pre-Test - Post-Test Control Group Design:

With this research design, test units are randomly assigned to experimental and control groups. A pre-test measure is taken from both groups.

Here is the standard notation for a Pre-Test - Post-Test Control Group study:

Selection bias is controlled by the randomized assignments of test units. Mortality can be a problem if it is not relatively equal between the experimental and control groups. History can also be an issue if these factors effect the experimental and control groups unequally.

The treatment effect or TE is measured by (O 2 O 1 ) - (O 4 O 3 ).

C. Solomon Four Group Design:

The Solomon Four Group Design is a research design that assesses the impact of pretesting on subsequent measures.[i] It is used when the researcher suspects that earlier tests influence the results of later tests. With this research design, test units are randomly allocated to two experimental groups and two control groups. One of the experimental groups and one of the control groups is measured. Both experimental groups are then exposed to a treatment. Afterwards, both experimental and control groups are measured. A total of six measurements are taken. The design aims to account for pre-testing bias and pre-test manipulation interaction bias.

Here is the standard notation for a Solomon Four Group study:

Quasi-Experimental Designs are used when the researcher creates an artificial environment to control for extraneous variables. With quasi-experimental designs, the research lacks control over when the treatment is administered or assigns test units to the experimental and control groups in a non-random fashion. There are two basic types of quasi-experimental designs: Time Series and Multiple Time Series.

A. Time Series: There is no randomization of the test units to the treatments. The timing of the treatment presentation as well as which test unites are exposed to the treatment may not be within the researcher's control. Consumer Attitude & Usage panels are an example of quasi-experimental designs using Time Series.

Here is the standard notation for a Time Series study:

The advantages of Time Series are that it is easier to interpret the results than a One Group Pre-Test - Post-Test design because of the many measures it takes. The multiple measures help determine underlying trends. But, the Time Series design has two weaknesses. First, researchers cannot control history. Second, given the repeated measures there is a testing effect on the subjects. Subjects may become more aware of their shopping habits, which could influence the results of the study.

B. Multiple Time Series: With the Multiple Time Series, the researchers add a control group to the research design. The addition of a control group enhances the researchers' ability to discern the treatment effect.

Here is the standard notation for a Multiple Time Series study:

Statistical Designs are a collection of basic experimental designs that offer researchers the ability to statistically control and analyze external variables. Statistical control uses various sophisticated statistical techniques to exclude the influence of extraneous variables from an analysis.

The most commonly used Statistical Research Designs are the Randomized Block Design, the Latin Square Design, and the Factorial Design. These designs offer the following advantages: 1) The effects of multiple independent variables on the dependent variable can be measured, 2) Specific extraneous variables can be statistically controlled, and each test unit can be measured more than once with these economically efficient designs. These designs are beyond the scope of an introductory Marketing Research class. We will not, therefore, cover them in any detail.

[i] Paul J. Lavraka. (2008). Encyclopedia of Survey Research Methods . http://srmo.sagepub.com/view/encyclopedia-of-survey-research-methods/n540.xml

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Advancing the Application and Use of Single-Case Research Designs: Reflections on Articles from the Special Issue

• SI: Advanced Quantitative Techniques for Single Case Experimental Design
• Published: 26 November 2021
• Volume 45 , pages 5–12, ( 2022 )

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• Robert H. Horner 1 &
• John Ferron 2  

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This special issue of Perspective on Behavior Science is a productive contribution to current advances in the use and documentation of single-case research designs. We focus in this article on major themes emphasized by the articles in this issue and suggest directions for improving professional standards focused on the design, analysis, and dissemination of single-case research.

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Beyond a Call to Action: An Introduction to the Special Issue on Diversity and Equity in the Practice of Behavior Analysis

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Rethinking the Place of Qualitative Methods in Behavior Analysis

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Aydin, O., & Yassikaya, M. Y. (this issue). Validity and reliability analysis of the Plot Digitizer Software Program for data extraction from single-case graphs. Perspectives on Behavior Science . Advance online publication. https://doi.org/10.1007/s40614.021.00284-0

Cox, A., Pritchard, D., Penney, H., Eiri, L., & Dyer, T. (this issue). Demonstrating an analyses of clinical data evaluating psychotropic medication reductions and the ACHIEVE! Program in adolescents with severe problem behavior. Perspectives on Behavior Science. Advance online publication. https://doi.org/10.1007/s40614-020-00279-3

Dowdy, A., Hantula, D., Travers, J. C., & Tincani, M. (this issue). Meta-analytic methods to detect publication bias in behavior science research. Perspectives on Behavior Science . Advance online publication. https://doi.org/10.1007/s40614-021-00303-0

Falligant, J., Kranak, M., & Hagopian, L. (this issue). Further analysis of advanced quantitative methods and supplemental interpretative aids with single-case experimental designs.

Fingerhut, J., Marbou, K., & Moeyaert, M. (2020). Single-case metric ranking tool (Version 1.2) [Microsoft Excel tool]. https://doi.org/10.17605/OSF.IO/7USBJ

Friedel, J., Cox A., Galizio, A., Swisher, M., Small, M., & Perez S. (this issue). Monte Carlo analyses for single-case experimental designs: An untapped resource for applied behavioral researchers and practitioners.

Gafurov, B. S., & Levin, J. R. (2021, June). ExPRT ( Excel Package of Randomization Tests): Statistical analyses of single-case intervention data (Version 4.2.1) [Computer software]. https://ex-prt.weebly.com

Institute of Education Sciences, National Center for Education Evaluation and Regional Assistance, & What Works Clearinghouse. (2020). What Works Clearinghouse Procedures Handbook (Vers. 4.1). https://ies.ed.gov/ncee/wwc/Docs/referenceresources/WWC-Procedures-Handboo v4-1508.pdf

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Kratochwill, T. R., Hitchcock, J., Horner, R. H., Levin, J. R., Odom, S. L., Rindskopf, D. M., & Shadish, W. R. (2010). Single-case designs technical documentation . What Works Clearinghouse . https://ies.ed.gov/ncee/wwc/pdf/wwc_scd.pdf

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Manolov, R., Tanious, R., & Onghena, P. (this issue-b). Quantitative techniques and graphical representations for interpreting results from alternating treatment design. Perspectives on Behavior Science . Advance online publication. https://doi.org/10.1007/s40614-021-00289-9

Mason, L., Otero, M., & Andrews, A. (this issue). Cochran’s Q test of stimulus overselectivity within the verbal repertoire of children with autism. Perspectives on Behavior Science . Advance online publication. https://doi.org/10.1007/s40614-021-00315-2

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Horner, R.H., Ferron, J. Advancing the Application and Use of Single-Case Research Designs: Reflections on Articles from the Special Issue. Perspect Behav Sci 45 , 5–12 (2022). https://doi.org/10.1007/s40614-021-00322-x

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Pre-experimental Design: Definition, Types & Examples

• October 1, 2021

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Experimental research is conducted to analyze and understand the effect of a program or a treatment. There are three types of experimental research designs – pre-experimental designs, true experimental designs, and quasi-experimental designs . 

In this blog, we will be talking about pre-experimental designs. Let’s first explain pre-experimental research. 

What is Pre-experimental Research?

As the name suggests, pre- experimental research happens even before the true experiment starts. This is done to determine the researchers’ intervention on a group of people. This will help them tell if the investment of cost and time for conducting a true experiment is worth a while. Hence, pre-experimental research is a preliminary step to justify the presence of the researcher’s intervention. 

The pre-experimental approach helps give some sort of guarantee that the experiment can be a full-scale successful study. 

What is Pre-experimental Design?

The pre-experimental design includes one or more than one experimental groups to be observed against certain treatments. It is the simplest form of research design that follows the basic steps in experiments. 

The pre-experimental design does not have a comparison group. This means that while a researcher can claim that participants who received certain treatment have experienced a change, they cannot conclude that the change was caused by the treatment itself. 

The research design can still be useful for exploratory research to test the feasibility for further study. 

Let us understand how pre-experimental design is different from the true and quasi-experiments:

The above table tells us pretty much about the working of the pre-experimental designs. So we can say that it is actually to test treatment, and check whether it has the potential to cause a change or not. For the same reasons, it is advised to perform pre-experiments to define the potential of a true experiment.

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Types of Pre-experimental Designs

Assuming now you have a better understanding of what the whole pre-experimental design concept is, it is time to move forward and look at its types and their working:

One-shot case study design

• This design practices the treatment of a single group.
• It only takes a single measurement after the experiment.
• A one-shot case study design only analyses post-test results.

The one-shot case study compares the post-test results to the expected results. It makes clear what the result is and how the case would have looked if the treatment wasn’t done. 

A team leader wants to implement a new soft skills program in the firm. The employees can be measured at the end of the first month to see the improvement in their soft skills. The team leader will know the impact of the program on the employees.

One-group pretest-posttest design

• Like the previous one, this design also works on just one experimental group.
• But this one takes two measures into account. 
• A pre-test and a post-test are conducted. 

As the name suggests, it includes one group and conducts pre-test and post-test on it. The pre-test will tell how the group was before they were put under treatment. Whereas post-test determines the changes in the group after the treatment. 

This sounds like a true experiment , but being a pre-experiment design, it does not have any control group. 

Following the previous example, the team leader here will conduct two tests. One before the soft skill program implementation to know the level of employees before they were put through the training. And a post-test to know their status after the training.

Now that he has a frame of reference, he knows exactly how the program helped the employees. 

Static-group comparison

• This compares two experimental groups.
• One group is exposed to the treatment.
• The other group is not exposed to the treatment.
• The difference between the two groups is the result of the experiment.

As the name suggests, it has two groups, which means it involves a control group too. 

In static-group comparison design, the two groups are observed as one goes through the treatment while the other does not. They are then compared to each other to determine the outcome of the treatment.

The team lead decides one group of employees to get the soft skills training while the other group remains as a control group and is not exposed to any program. He then compares both the groups and finds out the treatment group has evolved in their soft skills more than the control group. 

Due to such working, static-group comparison design is generally perceived as a quasi-experimental design too. 

Characteristics of Pre-experimental Designs

In this section, let us point down the characteristics of pre-experimental design:

• Generally uses only one group for treatment which makes observation simple and easy.
• Validates the experiment in the preliminary phase itself. 
• Pre-experimental design tells the researchers how their intervention will affect the whole study. 
• As they are conducted in the beginning, pre-experimental designs give evidence for or against their intervention.
• It does not involve the randomization of the participants. 
• It generally does not involve the control group, but in some cases where there is a need for studying the control group against the treatment group, static-group comparison comes into the picture. 
• The pre-experimental design gives an idea about how the treatment is going to work in case of actual true experiments.  

Validity of results in Pre-experimental Designs

Validity means a level to which data or results reflect the accuracy of reality. And in the case of pre-experimental research design, it is a tough catch. The reason being testing a hypothesis or dissolving a problem can be quite a difficult task, let’s say close to impossible. This being said, researchers find it challenging to generalize the results they got from the pre-experimental design, over the actual experiment. 

As pre-experimental design generally does not have any comparison groups to compete for the results with, that makes it pretty obvious for the researchers to go through the trouble of believing its results. Without comparison, it is hard to tell how significant or valid the result is. Because there is a chance that the result occurred due to some uncalled changes in the treatment, maturation of the group, or is it just sheer chance. 

Let’s say all the above parameters work just in favor of your experiment, you even have a control group to compare it with, but that still leaves us with one problem. And that is what “kind” of groups we get for the true experiments. It is possible that the subjects in your pre-experimental design were a lot different from the subjects you have for the true experiment. If this is the case, even if your treatment is constant, there is still going to be a change in your results. 

Advantages of Pre-experimental Designs

• Cost-effective due to its easy process. 
• Very simple to conduct.
• Efficient to conduct in the natural environment. 
• It is also suitable for beginners. 
• Involves less human intervention. 
• Determines how your treatment is going to affect the true experiment. 

Disadvantages of Pre-experimental Designs

• It is a weak design to determine causal relationships between variables. 
• Does not have any control over the research. 
• Possess a high threat to internal validity. 
• Researchers find it tough to examine the results’ integrity. 
• The absence of a control group makes the results less reliable. 

This sums up the basics of pre-experimental design and how it differs from other experimental research designs. Curious to learn how you can use survey software to conduct your experimental research, book a meeting with us . 

Explore all the survey question types possible on Voxco

Pre-experimental design is a research method that happens before the true experiment and determines how the researcher’s intervention will affect the experiment.

An example of a pre-experimental design would be a gym trainer implementing a new training schedule for a trainee.

Characteristics of pre-experimental design include its ability to determine the significance of treatment even before the true experiment is performed.

Researchers want to know how their intervention is going to affect the experiment. So even before the true experiment starts, they carry out a pre-experimental research design to determine the possible results of the true experiment.

The pre-experimental design deals with the treatment’s effect on the experiment and is carried out even before the true experiment takes place. While a true experiment is an actual experiment, it is important to conduct its pre-experiment first to see how the intervention is going to affect the experiment.

The true experimental design carries out the pre-test and post-test on both the treatment group as well as a control group. whereas in pre-experimental design, control group and pre-test are options. it does not always have the presence of those two and helps the researcher determine how the real experiment is going to happen.

The main difference between a pre-experimental design and a quasi-experimental design is that pre-experimental design does not use control groups and quasi-experimental design does. Quasi always makes use of the pre-test post-test model of result comparison while pre-experimental design mostly doesn’t.

Non-experimental research methods majorly fall into three categories namely: Cross-sectional research, correlational research and observational research.

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Roles Writing – review & editing

Affiliation Department of Biology, California State University, Northridge, Northridge, California, United States of America

• Xiaohan Kang, 
• Bruce Hajek, 
• Faqiang Wu, 
• Yoshie Hanzawa

• Published: October 31, 2019
• https://doi.org/10.1371/journal.pone.0224577
• See the preprint
• Peer Review
• Reader Comments

Many biological data sets are prepared using one-shot sampling, in which each individual organism is sampled at most once. Time series therefore do not follow trajectories of individuals over time. However, samples collected at different times from individuals grown under the same conditions share the same perturbations of the biological processes, and hence behave as surrogates for multiple samples from a single individual at different times. This implies the importance of growing individuals under multiple conditions if one-shot sampling is used. This paper models the condition effect explicitly by using condition-dependent nominal mRNA production amounts for each gene, it quantifies the performance of network structure estimators both analytically and numerically, and it illustrates the difficulty in network reconstruction under one-shot sampling when the condition effect is absent. A case study of an Arabidopsis circadian clock network model is also included.

Citation: Kang X, Hajek B, Wu F, Hanzawa Y (2019) Time series experimental design under one-shot sampling: The importance of condition diversity. PLoS ONE 14(10): e0224577. https://doi.org/10.1371/journal.pone.0224577

Editor: Steven M. Abel, University of Tennessee, UNITED STATES

Received: June 14, 2019; Accepted: October 16, 2019; Published: October 31, 2019

Copyright: © 2019 Kang et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: The computer simulation code is available at https://github.com/Veggente/one-shot-sampling .

Funding: This work was supported by the Plant Genome Research Program from the National Science Foundation (NSF-IOS-PGRP-1823145) to B.H. and Y.H.

Competing interests: The authors have declared that no competing interests exist.

Introduction

Time series data is important for studying biological processes in organisms because of the dynamic nature of the biological systems. Ideally it is desirable to use time series with multi-shot sampling , where each individual (such as a plant, animal, or microorganism) is sampled multiple times to produce the trajectory of the biological process, as in Fig 1 . Then the natural biological variations in different individuals can be leveraged for statistical inference, and thus inference can be made even if the samples are prepared under the same experimental condition.

• PPT PowerPoint slide
• PNG larger image
• TIFF original image

Each plant is observed four times.

https://doi.org/10.1371/journal.pone.0224577.g001

However, in many experiments multi-shot sampling is not possible. Due to stress response of the organisms and/or the large amount of cell tissue required for accurate measurements, the dynamics of the relevant biological process in an individual of the organism cannot be observed at multiple times without interference. For example, in an RNA-seq experiment an individual plant is often only sampled once in its entire life, leaving the dynamics unobserved at other times. See the Discussion section for a review of literature on this subject. We call the resulting time series data, as illustrated in Fig 2 , a time series with one-shot sampling . Because the time series with one-shot sampling do not follow the trajectories of the same individuals, they do not capture all the correlations in the biological processes. For example, the trajectory of observations on plants 1–2–3–4 and that on 1–6–7–4 in Fig 2 are statistically identical. The resulting partial observation renders some common models for the biological system dynamics inaccurate or even irrelevant.

Each plant is observed once.

https://doi.org/10.1371/journal.pone.0224577.g002

To address this problem, instead of getting multi-shot time series of single individuals, one can grow multiple individuals under each condition with a variety of conditions, and get one-shot time series of the single conditions. The one-shot samples from the same condition then become a surrogate for multi-shot samples for a single individual, as illustrated in Fig 3 . In essence, if we view the preparation condition of each sample as being random, then there should be a positive correlation among samples grown under the same condition. We call this correlation the condition variation effect . It is similar to the effect of biological variation of a single individual sampled at different times, if such sampling were possible.

https://doi.org/10.1371/journal.pone.0224577.g003

For each condition, the one-shot samples at different times are also complemented by biological replicates , which are samples from independent individuals taken at the same time used to reduce technical and/or biological variations. See the Discussion section for a review on how replicates are used for biological inference. With a budget over the number of samples, a balance must be kept between the number of conditions, the number of sampling times and the number of replicates.

To illustrate and quantify the effect of one-shot sampling in biological inference, we introduce a simple dynamic gene expression model with a condition variation effect. We consider a hypothesis testing setting and model the dynamics of the gene expression levels at different sampling times by a dynamic Bayesian network (DBN), where the randomness comes from nominal (or basal) biological and condition variations for each gene. The nominal condition-dependent variation of gene j is the same for all plants in that condition and the remaining variation is biological and is independent across the individuals in the condition. In contrast to GeneNetWeaver [ 1 ], where the effect of a condition is modeled by a random perturbation to the network coefficients, in our model the condition effect is characterized by correlation in the nominal variation terms of the dynamics. Note in both models samples from different individuals under the same condition are statistically independent given the randomness associated with the condition.

The contributions of this paper are threefold.

• A composite hypothesis testing problem on the gene regulatory network is formulated and a gene expression dynamic model that explicitly captures the per-gene condition effect and the gene regulatory interactions is proposed.
• The performance of gene regulatory network structure estimators is analyzed for both multi-shot and one-shot sampling, with focus on two algorithms. Furthermore, single-gene and multi-gene simulation results indicate that multiple-condition experiments can somewhat mitigate the shortcomings of one-shot sampling.
• The difficulty of network reconstruction under one-shot sampling with no condition effect is illustrated. This difficulty connects network analysis and differential expression analysis, two common tasks in large-scale genomics studies, in the sense that the part of network involving non-differentially expressed genes may be harder to reconstruct.

The simulation code for generating the figures is available at [ 2 ].

Materials and methods

Stochastic model of time-series samples.

This section formulates the hypothesis testing problem of learning the structure of the gene regulatory network (GRN) from gene expression data with one-shot or multi-shot sampling. The GRN is characterized by an unknown adjacency matrix. Given the GRN, a dynamic Bayesian network model is used for the gene expression evolution with time. Two parameters σ co, j and σ bi, j are used for each gene j , with the former explicitly capturing the condition variation effect and the latter capturing the biological variation level.

Model for gene regulatory network topology.

Model for gene expression dynamics.

This section models the gene expression dynamics of individuals by a dynamic Bayesian networks with parameters σ co, j and σ bi, j as the condition variation level and biological variation level for gene j .

Model for sampling method.

In this section two sampling methods are described: one-shot sampling and multi-shot sampling. For simplicity, throughout this paper we consider a full factorial design with CRT samples obtained under C conditions, R replicates and T sampling times, denoted by Y = ( Y c , r , t ) ( c , r , t )∈[ C ]×[ R ]×[ T ] . In other words, instead of X we observe Y , a noisy and possibly partial observation of X . Here the triple index for each sample indicates the condition, replicate, and time. As we will see in the Discussion at the end of this section, for either sampling method, the biological variation level σ bi, j can be reduced by combining multiple individuals to form a single sample.

Multi-shot sampling.

One-shot sampling.

Discussion on sources of variance.

• If the samples of the individuals under many different conditions are averaged and treated as a single sample, then effectively σ co, j , σ bi, j and σ te, j are reduced.

• If material from multiple individuals grown under the same condition is combined into a composite sample before measuring, then effectively σ bi, j is reduced while σ co, j and σ te, j remain unchanged. Note for microorganisms a sample may consist of millions of individuals and the biological variation is practically eliminated ( σ bi, j ≈ 0).
• If the samples from same individuals (technical replicates) are averaged and treated as a single sample, then effectively σ te, j is reduced while σ co, j and σ bi, j remain unchanged.

Note this sampling model with hierarchical driving and observational noises can also be used for single-cell RNA sequencing (scRNAseq) in addition to bulk RNA sequencing and microarray experiments. For scRNAseq, σ co, j can model the tissue-dependent variation (the global effect) and σ bi, j the per-cell variation (the local effect).

Performance evaluation of network structure estimators

This section studies the performance of network structure estimators with multi-shot and one-shot sampling data. First, general properties of the two sampling methods are obtained. Then two algorithms, the generalized likelihood-ratio test (GLRT) and the basic sparse linear regression (BSLR), are studied. The former is a standard decision rule for composite hypothesis testing problems and is shown to have some properties but is computationally infeasible for even a small number of genes. The latter is an algorithm based on linear regression, and is feasible for a moderate number of genes. Finally simulation results for a single-gene network with GLRT and for a multi-gene network with BSLR are shown.

General properties.

By ( 3 ), ( 4 ) and ( 5 ), the samples Y are jointly Gaussian with zero mean. The covariance of the random tensor Y is derived under the two sampling methods in the following.

• If Σ bi = 0 and C , R and T are fixed, the joint distribution of the data is the same for both types of sampling. So the performance of the estimator would be the same for multi-shot and one-shot sampling.
• If Σ bi = 0 and Σ te = 0 (no observation noise) and C , T are fixed, the joint distribution of the data is the same for both types of sampling (as noted in item 1) and any replicates beyond the first are identical to the first. So the performance of the estimator can be obtained even if all replicates beyond the first are discarded.
• Under multi-shot sampling, when C , R , T are fixed with R = 1, the joint distribution of the data depends on Σ co and Σ bi only through their sum. So the performance of the estimator would be the same for all Σ co and Σ bi such that Σ co + Σ bi is the same.

Network reconstruction algorithms.

In this section we introduce GLRT and BSLR. GLRT is a standard choice in composite hypothesis testing setting. We observe some properties for GLRT under one-shot and multi-shot sampling. However, GLRT involves optimizing the likelihood over the entire parameter space, which grows exponentially with the square of the number of genes. Hence GLRT is hard to compute for multiple-gene network reconstruction. In contrast, BSLR is an intuitive algorithm based on linear regression, and will be shown in simulations to perform reasonably well for multi-gene scenarios.

Proposition 1 GLRT ( with the knowledge of Σ co , Σ bi and Σ te ) has the following properties .

• Under one-shot sampling and Σ co = 0, the log likelihood of the data as a function of A ( i . e . the log likelihood function ) is invariant with respect to replacing A by − A . So , for the single-gene n = 1 case , the log likelihood function is an even function of A , and thus the GLRT will do no better than random guessing .

For 2 it suffices to notice in ( 6 ) the covariance is invariant with respect to changing A to − A . A proof of 1 is given below.

Proof of 1) We first prove it for the case of a single gene with constant T and a constant number of individuals, CR . To do that we need to look at the likelihood function closely.

In BSLR, replicates are averaged and the average gene expression levels at different times under different conditions are fitted in a linear regression model with best-subset sparse model selection, followed by a Granger causality test to eliminate the false discoveries. BSLR is similar to other two-stage linear regression–based network reconstruction algorithms, notably oCSE [ 4 ] and CaSPIAN [ 5 ]. Both oCSE and CaSPIAN use greedy algorithms in the first build-up stage, making them more suitable for large-scale problems. In contrast, BSLR uses best subset selection, which is conceptually simpler but computationally expensive for large n . For the tear-down stage both BSLR and CaSPIAN use the Granger causality test, while oCSE uses a permutation test.

Build-up stage.

A naive algorithm to solve the above optimization has a computational complexity of O ( n k +1 ) for fixed k as n → ∞. Faster near-optimal alternatives exist [ 6 ].

Tear-down stage.

Simulations on single-gene network reconstruction.

https://doi.org/10.1371/journal.pone.0224577.g004

The numerical simulations reflect the following observations implied by the analytical model.

• Under one-shot sampling, when γ = 0, the GLRT is equivalent to random guessing.
• The GLRT performs the same under one-shot and multi-shot sampling when γ = 1.
• Under no observation noise, the performance for multi-shot sampling is the same for all γ < 1.

Some empirical observations are in order.

• Multi-shot sampling outperforms one-shot sampling (unless γ = 1, where they have the same error probability).
• For one-shot sampling, the performance improves as γ increases. Regarding the number of replicates R per condition, if γ = 0.2 (small condition effect), a medium number of replicates (2 to 5) outperforms the single replicate strategy. For larger γ , one replicate per condition is the best.
• For multi-shot sampling, performance worsens as γ increases. One replicate per condition ( R = 1) is best.
• Comparing Fig 4a–4d vs. Fig 4e–4h , we observe that the performance degrades with the addition of observation noise, though for moderate noise ( σ te = 1.0) the effect of observation noise on the sign error is not large. Also, the effect of the algorithm not knowing γ is not large.

Simulations on multi-gene network reconstruction.

This subsection studies the case when multiple genes interact through the GRN. The goal is to compare one-shot vs. multi-shot sampling for BSLR under a variety of scenarios, including different homogeneous γ values, varying number of replicates, varying observation noise level, and heterogeneous γ values.

The performance evaluation for multi-gene network reconstruction is trickier than the single-gene case because of the many degrees of freedom introduced by the number of genes. First, the network adjacency matrix A is now an n -by- n matrix. While some notion of “size” of A (like the spectral radius or the matrix norm) may be important, potentially every entry of A may affect the reconstruction result. So instead of fixing a ground truth A as in Fig 4 , we fix a prior distribution of A with split Gaussian prior described in S2 Appendix (note we assume the knowledge of no autoregulation), and choose A i.i.d. from the prior distribution with d max = 3. Second, because the prior of A can be subject to sparsity constraints and thus far from a uniform distribution, multiple loss functions that are more meaningful than the ternary error rate can be considered for performance. So we consider ternary FDR, ternary FNR and ternary FPR for the multi-gene case. In the simulations we have 20 genes and d max = 3 with in-degree uniformly distributed over {0, 1, …, d max }, so the average in-degree is 1.5. The number of sampling times is T = 6 and CR = 30.

Varying γ , R and σ te .

In this set of simulations we fix the observation noise level and vary the number of replicates R and the condition correlation coefficient γ . The performance of BSLR under one-shot and multi-shot sampling is shown in Fig 5 ( σ te = 0) and Fig 6 ( σ te = 1). Note BSLR does not apply to a single condition with 30 replicates due to the constraint that the degrees of freedom C ( T − 1) − k − 2 in the second stage must be at least 1.

https://doi.org/10.1371/journal.pone.0224577.g005

https://doi.org/10.1371/journal.pone.0224577.g006

For multi-shot sampling, in the noiseless case, we see all three losses are invariant with respect to different γ for fixed R , which is consistent with property 4 in the section on general properties because BSLR is an average-based scale-invariant algorithm (note CR is a constant so for different R the performance is different due to the change in C ). In the noisy case, the FDR and FNR slightly decrease as γ increases, which is an opposite trend compared with Fig 4f and 4h .

In summary, the main conclusions from Figs 5 and 6 are the following.

• The performance of BSLR under multi-shot sampling is consistently better than that under one-shot sampling.
• The performance of BSLR under one-shot sampling varies with γ , from random guessing performance at γ = 0 to the same performance as multi-shot sampling at γ = 1.
• By comparing Figs 5 with 6 , we see the observation noise of σ te = 1 has only a small effect on the performance with the two sampling methods.

Reduced number of directly differentially expressed genes.

https://doi.org/10.1371/journal.pone.0224577.g007

We summarize the simulations performed in Table 1 . Note the last row is a summary of Table 2 in the Discussion section.

OS and MS stand for the losses of one-shot sampling and multi-shot sampling. RG stands for random guessing. * indicates mathematically proved results.

https://doi.org/10.1371/journal.pone.0224577.t001

The errors are estimated using Hoeffding’s inequality over 1000 simulations with significance level 0.05.

https://doi.org/10.1371/journal.pone.0224577.t002

Information limitation for reconstruction under one shot sampling without condition effect

In the previous section it is shown that both GLRT and BSLR are close to random guessing under one-shot sampling when σ co, j = 0 for all j . This leads us to the following question: is the network reconstruction with no condition effect ( σ co, j = 0 for all j ) information theoretically possible? In this section we examine this question under general estimator-independent settings. Note in this case the trajectories of all individuals are independent given A regardless of ( c k ) k ∈[ K ] .

As we have seen in Proposition 1 part 2, when Σ co = 0, the distribution of the observed data Y is invariant under adjacency matrix A or − A , implying any estimator will have a sign error probability no better than random guessing for the average or worst case over A and − A . Here, instead of sign error probability, we consider the estimation for A itself.

The extreme case with infinite number of samples available for network reconstruction is considered to give a lower bound on the accuracy for the finite data case. Note that with infinite number of samples a sufficient statistic for the estimation of the parameter A is the marginal distributions of X 1 ( t ); no information on the correlation of ( X 1 ( t )) t ∈[ T ] across time t can be obtained. A similar observation is made in [ 7 ] for sampling stochastic differential equations.

In summary, the recovery of the matrix A is generally not possible in the stationary case, and also not possible in the transient case at least when A is orthogonal. To reconstruct A , further constraints (like sparsity) may be required.

One-shot sampling in the literature

This section reviews the sampling procedures reported in several papers measuring gene expression levels in biological organisms with samples collected at different times to form time series data. In all cases, the sampling is one-shot, in the sense that a single plant or cell is only sampled at one time.

Microorganisms.

In the transcriptional network inference challenge from DREAM5 [ 8 ], three compendia of biological data sets were provided based on microorganisms ( E. coli , S. aureus , and S. cerevisiae ), and some of the data corresponded to different sampling times in a time series. Being based on microorganisms, the expression level measurements involved multiple individuals per sample, a form of one-shot sampling.

In [ 9 ], the plants are exposed to nitrate, which serves as a synchronizing event, and samples are taken from three to twenty minutes after the synchronizing event. The statement “… each replicate is independent of all microarrays preceding and following in time” suggests the experiments are based on one-shot sampling. In contrast, the state-space model with correlation between transcription factors in an earlier time and the regulated genes in a later time fits multi-shot sampling. [ 10 ] studied the gene expression difference between leaves at different developmental stages in rice. The 12th, 11th and 10th leaf blades were collected every 3 days for 15 days starting from the day of the emergence of the 12th leaves. While a single plant could provide multiple samples, namely three different leaves at a given sampling time, no plant was sampled at two different times. Thus, from the standpoint of producing time series data, the sampling in this paper was one-shot sampling. [ 11 ] devised the phenol-sodium dodecyl sulfate (SDS) method for isolating total RNA from Arabidopsis . It reports the relative level of mRNA of several genes for five time points ranging up to six hours after exposure to a synchronizing event, namely being sprayed by a hormone trans -zeatin. The samples were taken from the leaves of plants. It is not clear from the paper whether the samples were collected from different leaves of the same plant, or from leaves of different plants.

[ 12 ] likely used one-shot sampling for their −24, 60, 120, 168 hour time series data from mouse skeletal muscle C2C12 cells without specifying whether the samples are all taken from different individuals. [ 13 ] produced time series data by extracting cells from a human, seeding the cells on plates, and producing samples in triplicate, at a series of six times, for each of five conditions. Multiple cells are used for each sample with different sets of cells being used for different samples, so this is an example of one-shot sampling of in vitro experiment in the sense that each plate of cells is one individual. The use of (five) multiple conditions can serve as a surrogate for a single individual set of cells to gain the effect of multi-shot sampling. Similarly, the data sets produced by [ 14 ] involving the plating of HeLa S3 cells can be classified as one-shot samples because different samples are made from different sets of individual cells. Interestingly, the samples are prepared under one set of conditions, so the use of different conditions is not adopted as a surrogate for multi-shot sampling. However, a particular line of cells was selected (HeLa S3) for which cells can be highly synchronized. Also, the paper does not attempt to determine causal interactions.

The three in silico benchmark suites described in the GeneNetWeaver paper on performance profiling of network inference methods [ 1 ] consisted of steady state, and therefore one-shot, samples from dynamical models. However, the GeneNetWeaver software can be used to generate multi-shot time series data, and some of that was included in the network inference challenges, DREAM3, DREAM4, and DREAM5 [ 1 , 8 ].

On biological replicates

In many biological experiments, independent biological replicates are used to reduce the variation in the measurements and to consequently increase the power of the statistical tests. It turns out that both how to use biological replicates, and the power of biological replicates, depend on whether the sampling is one-shot or multi-shot. To focus on this issue we first summarize how replicates have traditionally been used for the more common problem of gene differential expression analysis, before turning to the use of replicates for recovery of gene regulatory networks.

The following summarizes the use of replicates for gene differential expression analysis. A recent survey [ 15 ] suggests a minimum of three replicates for RNA-seq experiments whenever sample availability allows. Briggs et al. [ 16 ] studies the effect of biological replication together with dye switching in microarray experiments and recommends biological replication when precision in the measurements is desired. Liu et al. [ 17 ] studies the tradeoff between biological replication and sequencing depth under a sequencing budget limit in RNA-seq differential expression (DE) analysis. It proposes a metric for cost effectiveness that suggests a sequencing depth of 10 million reads per library of human breast cells and 2–6 biological replicates for optimal RNA-seq DE design. Schurch et al. [ 18 ] studies the number of necessary biological replicates in RNA-seq differential expression experiments on S. cerevisiae quantitatively with various statistical tools and concludes with the usage of a minimum of six biological replicates.

For regulatory network reconstruction there is even less consensus on how replicates should be used. One straightforward way is to reduce the replicates into a single set of data by averaging either directly or after a random resampling of the original replicated data. In this case the mean of the replicates are used as a better estimate of the population than each single replicate, while higher moments of the empirical distribution of the replicates are practically ignored. Another way adopted in [ 9 ] is to account for all four potential transitions between two replicates in two adjacent sampling times in their machine learning algorithm due to the one-shot nature of the replicates. In the next section, we illustrate why replicates should be used differently for one-shot and multi-shot sampling, in the context of recovering a circadian clock network model.

A case study on Arabidopsis circadian clock network

As we have discussed earlier, the current expression datasets are prominently one-shot, making a direct comparison between one-shot and multi-shot sampling in real biological data difficult. The lack of a well-accepted ground truth of the gene regulatory network also makes performance evaluation hard, if not impossible. To test the applicability of the sampling models on real biological data, we generate expression data from a most-accepted Arabidopsis circadian clock model using stochastic differential equation (SDE) model similar to GeneNetWeaver with condition-dependent Brownian motions, and evaluate the performance of BSLR.

https://doi.org/10.1371/journal.pone.0224577.g008

In summary, we demonstrated a setting of the biologically plausible Arabidopsis circadian clock network with a single condition, where the BSLR performs similarly to a random guessing algorithm under one-shot sampling, and performs significantly better under multi-shot sampling. We also show that whether replicate averaging should be done or not varies with the sampling method.

Conclusions

One-shot sampling can miss a lot of potentially useful correlation information. Often gene expression data collected from plants is prepared under one-shot sampling. One factor that can partially mitigate the shortcomings of one-shot sampling is to prepare samples under a variety of conditions or perturbations. One-shot samples grown under the same condition can then be thought of as a surrogate for the multi-shot samples of an individual plant.

To clarify issues and take a step towards quantifying them, we proposed a gene expression dynamic model for gene regulatory network reconstruction that explicitly captures the condition variation effect. We show analytically and numerically the performance of two algorithms for single-gene and multi-gene settings. We also demonstrate the difficulty of network reconstruction without condition variation effect.

There is little agreement across the biology literature about how to model the impact of condition on the gene regulatory network. In some cases, it is not even clear that we are observing the same network structure as conditions vary. Nevertheless, our results suggest that the preparation of samples under different conditions can partially compensate for the shortcomings of one-shot sampling.

Supporting information

S1 appendix. joint estimation for single-gene autoregulation recovery..

The parameters A , γ , σ , and σ te are assumed unknown and jointly estimated in GLRT.

https://doi.org/10.1371/journal.pone.0224577.s001

S2 Appendix. Split Gaussian network prior.

The random network prior distribution used to generate the multi-gene network.

https://doi.org/10.1371/journal.pone.0224577.s002

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Neag School of Education

Educational Research Basics by Del Siegle

Experimental research designs.

R=Random Assignment X= Treatment O=Observation (Assessment)

R = Random Assignment X = Treatment O = Observation (test or measurement of some type)

Del Siegle, Ph.D. Neag School of Education – University of Connecticut [email protected] www.delsiegle.com

• Experimental Research Designs: Types, Examples & Methods

Experimental research is the most familiar type of research design for individuals in the physical sciences and a host of other fields. This is mainly because experimental research is a classical scientific experiment, similar to those performed in high school science classes.

Imagine taking 2 samples of the same plant and exposing one of them to sunlight, while the other is kept away from sunlight. Let the plant exposed to sunlight be called sample A, while the latter is called sample B.

If after the duration of the research, we find out that sample A grows and sample B dies, even though they are both regularly wetted and given the same treatment. Therefore, we can conclude that sunlight will aid growth in all similar plants.

What is Experimental Research?

Experimental research is a scientific approach to research, where one or more independent variables are manipulated and applied to one or more dependent variables to measure their effect on the latter. The effect of the independent variables on the dependent variables is usually observed and recorded over some time, to aid researchers in drawing a reasonable conclusion regarding the relationship between these 2 variable types.

The experimental research method is widely used in physical and social sciences, psychology, and education. It is based on the comparison between two or more groups with a straightforward logic, which may, however, be difficult to execute.

Mostly related to a laboratory test procedure, experimental research designs involve collecting quantitative data and performing statistical analysis on them during research. Therefore, making it an example of quantitative research method .

What are The Types of Experimental Research Design?

The types of experimental research design are determined by the way the researcher assigns subjects to different conditions and groups. They are of 3 types, namely; pre-experimental, quasi-experimental, and true experimental research.

Pre-experimental Research Design

In pre-experimental research design, either a group or various dependent groups are observed for the effect of the application of an independent variable which is presumed to cause change. It is the simplest form of experimental research design and is treated with no control group.

Although very practical, experimental research is lacking in several areas of the true-experimental criteria. The pre-experimental research design is further divided into three types

• One-shot Case Study Research Design

In this type of experimental study, only one dependent group or variable is considered. The study is carried out after some treatment which was presumed to cause change, making it a posttest study.

• One-group Pretest-posttest Research Design: 

This research design combines both posttest and pretest study by carrying out a test on a single group before the treatment is administered and after the treatment is administered. With the former being administered at the beginning of treatment and later at the end.

• Static-group Comparison: 

In a static-group comparison study, 2 or more groups are placed under observation, where only one of the groups is subjected to some treatment while the other groups are held static. All the groups are post-tested, and the observed differences between the groups are assumed to be a result of the treatment.

Quasi-experimental Research Design

  The word “quasi” means partial, half, or pseudo. Therefore, the quasi-experimental research bearing a resemblance to the true experimental research, but not the same.  In quasi-experiments, the participants are not randomly assigned, and as such, they are used in settings where randomization is difficult or impossible.

 This is very common in educational research, where administrators are unwilling to allow the random selection of students for experimental samples.

Some examples of quasi-experimental research design include; the time series, no equivalent control group design, and the counterbalanced design.

True Experimental Research Design

The true experimental research design relies on statistical analysis to approve or disprove a hypothesis. It is the most accurate type of experimental design and may be carried out with or without a pretest on at least 2 randomly assigned dependent subjects.

The true experimental research design must contain a control group, a variable that can be manipulated by the researcher, and the distribution must be random. The classification of true experimental design include:

• The posttest-only Control Group Design: In this design, subjects are randomly selected and assigned to the 2 groups (control and experimental), and only the experimental group is treated. After close observation, both groups are post-tested, and a conclusion is drawn from the difference between these groups.
• The pretest-posttest Control Group Design: For this control group design, subjects are randomly assigned to the 2 groups, both are presented, but only the experimental group is treated. After close observation, both groups are post-tested to measure the degree of change in each group.
• Solomon four-group Design: This is the combination of the pretest-only and the pretest-posttest control groups. In this case, the randomly selected subjects are placed into 4 groups.

The first two of these groups are tested using the posttest-only method, while the other two are tested using the pretest-posttest method.

Examples of Experimental Research

Experimental research examples are different, depending on the type of experimental research design that is being considered. The most basic example of experimental research is laboratory experiments, which may differ in nature depending on the subject of research.

Administering Exams After The End of Semester

During the semester, students in a class are lectured on particular courses and an exam is administered at the end of the semester. In this case, the students are the subjects or dependent variables while the lectures are the independent variables treated on the subjects.

Only one group of carefully selected subjects are considered in this research, making it a pre-experimental research design example. We will also notice that tests are only carried out at the end of the semester, and not at the beginning.

Further making it easy for us to conclude that it is a one-shot case study research. 

Employee Skill Evaluation

Before employing a job seeker, organizations conduct tests that are used to screen out less qualified candidates from the pool of qualified applicants. This way, organizations can determine an employee’s skill set at the point of employment.

In the course of employment, organizations also carry out employee training to improve employee productivity and generally grow the organization. Further evaluation is carried out at the end of each training to test the impact of the training on employee skills, and test for improvement.

Here, the subject is the employee, while the treatment is the training conducted. This is a pretest-posttest control group experimental research example.

Evaluation of Teaching Method

Let us consider an academic institution that wants to evaluate the teaching method of 2 teachers to determine which is best. Imagine a case whereby the students assigned to each teacher is carefully selected probably due to personal request by parents or due to stubbornness and smartness.

This is a no equivalent group design example because the samples are not equal. By evaluating the effectiveness of each teacher’s teaching method this way, we may conclude after a post-test has been carried out.

However, this may be influenced by factors like the natural sweetness of a student. For example, a very smart student will grab more easily than his or her peers irrespective of the method of teaching.

What are the Characteristics of Experimental Research?  

Experimental research contains dependent, independent and extraneous variables. The dependent variables are the variables being treated or manipulated and are sometimes called the subject of the research.

The independent variables are the experimental treatment being exerted on the dependent variables. Extraneous variables, on the other hand, are other factors affecting the experiment that may also contribute to the change.

The setting is where the experiment is carried out. Many experiments are carried out in the laboratory, where control can be exerted on the extraneous variables, thereby eliminating them. 

Other experiments are carried out in a less controllable setting. The choice of setting used in research depends on the nature of the experiment being carried out.

• Multivariable

Experimental research may include multiple independent variables, e.g. time, skills, test scores, etc.

Why Use Experimental Research Design?  

Experimental research design can be majorly used in physical sciences, social sciences, education, and psychology. It is used to make predictions and draw conclusions on a subject matter. 

Some uses of experimental research design are highlighted below.

• Medicine: Experimental research is used to provide the proper treatment for diseases. In most cases, rather than directly using patients as the research subject, researchers take a sample of the bacteria from the patient’s body and are treated with the developed antibacterial

The changes observed during this period are recorded and evaluated to determine its effectiveness. This process can be carried out using different experimental research methods.

• Education: Asides from science subjects like Chemistry and Physics which involves teaching students how to perform experimental research, it can also be used in improving the standard of an academic institution. This includes testing students’ knowledge on different topics, coming up with better teaching methods, and the implementation of other programs that will aid student learning.
• Human Behavior: Social scientists are the ones who mostly use experimental research to test human behaviour. For example, consider 2 people randomly chosen to be the subject of the social interaction research where one person is placed in a room without human interaction for 1 year.

The other person is placed in a room with a few other people, enjoying human interaction. There will be a difference in their behaviour at the end of the experiment.

• UI/UX: During the product development phase, one of the major aims of the product team is to create a great user experience with the product. Therefore, before launching the final product design, potential are brought in to interact with the product.

For example, when finding it difficult to choose how to position a button or feature on the app interface, a random sample of product testers are allowed to test the 2 samples and how the button positioning influences the user interaction is recorded.

What are the Disadvantages of Experimental Research?  

• It is highly prone to human error due to its dependency on variable control which may not be properly implemented. These errors could eliminate the validity of the experiment and the research being conducted.
• Exerting control of extraneous variables may create unrealistic situations. Eliminating real-life variables will result in inaccurate conclusions. This may also result in researchers controlling the variables to suit his or her personal preferences.
• It is a time-consuming process. So much time is spent on testing dependent variables and waiting for the effect of the manipulation of dependent variables to manifest.
• It is expensive. 
• It is very risky and may have ethical complications that cannot be ignored. This is common in medical research, where failed trials may lead to a patient’s death or a deteriorating health condition.
• Experimental research results are not descriptive.
• Response bias can also be supplied by the subject of the conversation.
• Human responses in experimental research can be difficult to measure. 

What are the Data Collection Methods in Experimental Research?  

Data collection methods in experimental research are the different ways in which data can be collected for experimental research. They are used in different cases, depending on the type of research being carried out.

1. Observational Study

This type of study is carried out over a long period. It measures and observes the variables of interest without changing existing conditions.

When researching the effect of social interaction on human behavior, the subjects who are placed in 2 different environments are observed throughout the research. No matter the kind of absurd behavior that is exhibited by the subject during this period, its condition will not be changed.

This may be a very risky thing to do in medical cases because it may lead to death or worse medical conditions.

2. Simulations

This procedure uses mathematical, physical, or computer models to replicate a real-life process or situation. It is frequently used when the actual situation is too expensive, dangerous, or impractical to replicate in real life.

This method is commonly used in engineering and operational research for learning purposes and sometimes as a tool to estimate possible outcomes of real research. Some common situation software are Simulink, MATLAB, and Simul8.

Not all kinds of experimental research can be carried out using simulation as a data collection tool . It is very impractical for a lot of laboratory-based research that involves chemical processes.

A survey is a tool used to gather relevant data about the characteristics of a population and is one of the most common data collection tools. A survey consists of a group of questions prepared by the researcher, to be answered by the research subject.

Surveys can be shared with the respondents both physically and electronically. When collecting data through surveys, the kind of data collected depends on the respondent, and researchers have limited control over it.

Formplus is the best tool for collecting experimental data using survey s. It has relevant features that will aid the data collection process and can also be used in other aspects of experimental research.

Differences between Experimental and Non-Experimental Research 

1. In experimental research, the researcher can control and manipulate the environment of the research, including the predictor variable which can be changed. On the other hand, non-experimental research cannot be controlled or manipulated by the researcher at will.

This is because it takes place in a real-life setting, where extraneous variables cannot be eliminated. Therefore, it is more difficult to conclude non-experimental studies, even though they are much more flexible and allow for a greater range of study fields.

2. The relationship between cause and effect cannot be established in non-experimental research, while it can be established in experimental research. This may be because many extraneous variables also influence the changes in the research subject, making it difficult to point at a particular variable as the cause of a particular change

3. Independent variables are not introduced, withdrawn, or manipulated in non-experimental designs, but the same may not be said about experimental research.

Conclusion  

Experimental research designs are often considered to be the standard in research designs. This is partly due to the common misconception that research is equivalent to scientific experiments—a component of experimental research design.

In this research design, one or more subjects or dependent variables are randomly assigned to different treatments (i.e. independent variables manipulated by the researcher) and the results are observed to conclude. One of the uniqueness of experimental research is in its ability to control the effect of extraneous variables.

Experimental research is suitable for research whose goal is to examine cause-effect relationships, e.g. explanatory research. It can be conducted in the laboratory or field settings, depending on the aim of the research that is being carried out. 

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2. The “One Shot” Case Study Revisited

Method. Thousand Oaks, CA: Pine Forge Press.———.(2000). Fuzzy Set Social Science. Chicago, IL: University of Chicago Press. Ragin, Charles C. and Howard Becker, eds.(1992). What Is a Case? Exploring the Foundations of Social Inquiry. Cambridge, UK: Cambridge University Press. Savolainen, Jukka.(1994).“The Rationality of Drawing Big Conclusions Based on Small Samples: In Defense of Mill's Methods.” Social Forces 72 (2), 1217–1224. Stinchcombe, Arthur.(1968). Constructing Social Theories.

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Ip S, Paulus JK, Balk EM, et al. Role of Single Group Studies in Agency for Healthcare Research and Quality Comparative Effectiveness Reviews [Internet]. Rockville (MD): Agency for Healthcare Research and Quality (US); 2013 Jan.

Role of Single Group Studies in Agency for Healthcare Research and Quality Comparative Effectiveness Reviews [Internet].

Evidence from randomized controlled trials is often unavailable or insufficient to answer all questions posed in a comparative effectiveness review (CER). Thus, following a best-available-evidence approach, 1 systematic reviewers often use observational studies including a comparison group to examine the comparative effectiveness and safety of alternative therapeutic strategies. However, there are many instances where even observational studies with a comparison group are unavailable. Therefore, single group studies—those that evaluate a single intervention given to all subjects included in the study design—are often part of the evidence available to systematic reviewers conducting CERs.

We define a single group study as a study that consists of only a single group of subjects included in the study design, in which all subjects received a single intervention and the outcomes are assessed over time (i.e., not a cross-sectional study). These studies may be prospective or retrospective cohort studies. A number of study types would be included in this category, including investigations described as “single arm studies,” case series, registries, “before-after designs,” and time series studies. A classification scheme developed by Campbell and Stanley describes two single group studies consistent with our definition: the “one-shot case study” and the “one-group pretest–post-test design.” 2 In the one-shot case study, a single group is studied only once after a treatment is applied. In the one-group pretest–post-test design, a pretest evaluation is followed by a treatment and then a post-test. For the rest of this paper, we will use the simplified term “single group study” when describing these designs in general.

Single group studies are often conducted in the setting of strong therapy preferences (e.g., hyperbaric oxygen therapy for arterial gas embolism 3 ). This is especially true for transplantation studies of vital organs in the setting of rapid and fatal disease progression. For example, in patients with end-stage liver disease, the natural history of disease is so well known that it would be difficult to carry out a trial with an untransplanted study arm. Also, a field of clinical inquiry that is relatively new may not be sufficiently mature to rationalize a comparative hypothesis. For example, novel procedures or drugs are often initially evaluated in single group studies that are used to inform the design of a subsequent study with an internal comparison group.

Single group study designs are commonly used to monitor adverse events that may become evident only with long-term followup of large numbers of treated patients, which is not practical or efficient with other study designs. For example, phase 4 studies to monitor postmarketing adverse events and evaluations of therapies often include a single group of patients managed with the same treatment strategy and followed over time. Open-label extensions of clinical trials present another type of clinical investigation that often lacks an internal, concurrent comparison group. Although they are designed to follow patients for an extended period of time, they also usually evaluate a more highly selected population of patients who completed the randomized trial, tolerated the medication, and agreed to participate in the extension. Expanded access programs (or “compassionate use”) allow the use of an investigational drug outside of a clinical trial to treat a patient with a serious or immediately life-threatening disease or condition lacking satisfactory alternative treatment options. These investigations commonly describe the experience of a single group of patients without a comparison group (for example, see Janne 2004 4 ). Finally, registries of patients who have been exposed to a single drug or device may also be assembled for monitoring long-term sequelae without an internal comparison group. An example includes the coordinated effort to study newly introduced devices through the Interagency Registry for Mechanically Assisted Circulatory Support, established to capture detailed clinical data on all patients receiving implantable ventricular assist pumps in the United States. 5

Since single group studies do not include a direct, concurrent comparison group, their role in informing comparative effectiveness questions is not straightforward. Observational study designs in general suffer from a potential lack of exchangeability of exposed and unexposed subjects. In other words, the outcome in the untreated group may differ from what would have occurred in the treated in the absence of treatment (the “counterfactual outcome”). The absence of a direct, concurrent untreated comparator in single group studies presents an added challenge to identifying a proxy for the counterfactual, or an answer to the question: “What would have been the treated person's experience if there had been no treatment?” Extrapolations based on the expected outcomes in the “missing” untreated arm are required for inference about treatment effects. In fact, explicit and implicit comparisons are frequently made in single group studies even in the absence of a direct, concurrent comparator. The appropriate interpretation of these implicit and explicit comparisons and their potential utility in CERs must include consideration of the key assumptions underlying each single group design.

The ability of observational studies to answer questions about the benefits or intended effects of pharmacotherapeutic agents, devices, or procedural interventions has been a matter of debate. 6 Guidance has been developed for systematic reviewers for decisionmaking on the inclusion of observational studies in general in CERs. 6 However, to the best of our knowledge, the use of single group observational studies in CERs has not been specifically addressed in this methods guide or elsewhere. While the value of using single group studies to identify and quantify the occurrence of harms a of interventions is well recognized, the role of these studies in evaluating comparative effectiveness and safety is not well developed. Given that single group studies may comprise a substantial portion of the evidence base for a given clinical question, and in light of the challenges in their interpretation and relevance to questions that are comparative in nature, it is important to clarify whether they are useful in informing comparative effectiveness assessments, and if so, to clarify the assumptions required to support their use.

In order to illuminate the use of single group studies in CERs, we conducted an empirical review of current practices in using single group studies in CERs conducted by Evidence-based Practice Centers (EPCs) for the Agency for Healthcare Research and Quality (AHRQ). The summary findings should serve as an impetus for future work in reaching a consensus across EPCs as to when and how single group studies should be used in CERs specifically and systematic reviews in general. In addition to the empirical review, we also provided a narrative review section describing the common single group study designs and the key considerations and assumptions required for their interpretation to help guide comparative effectiveness reviewers who encounter this type of evidence.

Includes adverse events of interventions as well as other harmful events that may be indirectly related to the intervention.

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What the data says about abortion in the u.s..

Pew Research Center has conducted many surveys about abortion over the years, providing a lens into Americans’ views on whether the procedure should be legal, among a host of other questions.

In a  Center survey  conducted nearly a year after the Supreme Court’s June 2022 decision that  ended the constitutional right to abortion , 62% of U.S. adults said the practice should be legal in all or most cases, while 36% said it should be illegal in all or most cases. Another survey conducted a few months before the decision showed that relatively few Americans take an absolutist view on the issue .

Find answers to common questions about abortion in America, based on data from the Centers for Disease Control and Prevention (CDC) and the Guttmacher Institute, which have tracked these patterns for several decades:

How many abortions are there in the U.S. each year?

How has the number of abortions in the u.s. changed over time, what is the abortion rate among women in the u.s. how has it changed over time, what are the most common types of abortion, how many abortion providers are there in the u.s., and how has that number changed, what percentage of abortions are for women who live in a different state from the abortion provider, what are the demographics of women who have had abortions, when during pregnancy do most abortions occur, how often are there medical complications from abortion.

This compilation of data on abortion in the United States draws mainly from two sources: the Centers for Disease Control and Prevention (CDC) and the Guttmacher Institute, both of which have regularly compiled national abortion data for approximately half a century, and which collect their data in different ways.

The CDC data that is highlighted in this post comes from the agency’s “abortion surveillance” reports, which have been published annually since 1974 (and which have included data from 1969). Its figures from 1973 through 1996 include data from all 50 states, the District of Columbia and New York City – 52 “reporting areas” in all. Since 1997, the CDC’s totals have lacked data from some states (most notably California) for the years that those states did not report data to the agency. The four reporting areas that did not submit data to the CDC in 2021 – California, Maryland, New Hampshire and New Jersey – accounted for approximately 25% of all legal induced abortions in the U.S. in 2020, according to Guttmacher’s data. Most states, though,  do  have data in the reports, and the figures for the vast majority of them came from each state’s central health agency, while for some states, the figures came from hospitals and other medical facilities.

Discussion of CDC abortion data involving women’s state of residence, marital status, race, ethnicity, age, abortion history and the number of previous live births excludes the low share of abortions where that information was not supplied. Read the methodology for the CDC’s latest abortion surveillance report , which includes data from 2021, for more details. Previous reports can be found at  stacks.cdc.gov  by entering “abortion surveillance” into the search box.

For the numbers of deaths caused by induced abortions in 1963 and 1965, this analysis looks at reports by the then-U.S. Department of Health, Education and Welfare, a precursor to the Department of Health and Human Services. In computing those figures, we excluded abortions listed in the report under the categories “spontaneous or unspecified” or as “other.” (“Spontaneous abortion” is another way of referring to miscarriages.)

Guttmacher data in this post comes from national surveys of abortion providers that Guttmacher has conducted 19 times since 1973. Guttmacher compiles its figures after contacting every known provider of abortions – clinics, hospitals and physicians’ offices – in the country. It uses questionnaires and health department data, and it provides estimates for abortion providers that don’t respond to its inquiries. (In 2020, the last year for which it has released data on the number of abortions in the U.S., it used estimates for 12% of abortions.) For most of the 2000s, Guttmacher has conducted these national surveys every three years, each time getting abortion data for the prior two years. For each interim year, Guttmacher has calculated estimates based on trends from its own figures and from other data.

The latest full summary of Guttmacher data came in the institute’s report titled “Abortion Incidence and Service Availability in the United States, 2020.” It includes figures for 2020 and 2019 and estimates for 2018. The report includes a methods section.

In addition, this post uses data from StatPearls, an online health care resource, on complications from abortion.

An exact answer is hard to come by. The CDC and the Guttmacher Institute have each tried to measure this for around half a century, but they use different methods and publish different figures.

The last year for which the CDC reported a yearly national total for abortions is 2021. It found there were 625,978 abortions in the District of Columbia and the 46 states with available data that year, up from 597,355 in those states and D.C. in 2020. The corresponding figure for 2019 was 607,720.

The last year for which Guttmacher reported a yearly national total was 2020. It said there were 930,160 abortions that year in all 50 states and the District of Columbia, compared with 916,460 in 2019.

• How the CDC gets its data: It compiles figures that are voluntarily reported by states’ central health agencies, including separate figures for New York City and the District of Columbia. Its latest totals do not include figures from California, Maryland, New Hampshire or New Jersey, which did not report data to the CDC. ( Read the methodology from the latest CDC report .)
• How Guttmacher gets its data: It compiles its figures after contacting every known abortion provider – clinics, hospitals and physicians’ offices – in the country. It uses questionnaires and health department data, then provides estimates for abortion providers that don’t respond. Guttmacher’s figures are higher than the CDC’s in part because they include data (and in some instances, estimates) from all 50 states. ( Read the institute’s latest full report and methodology .)

While the Guttmacher Institute supports abortion rights, its empirical data on abortions in the U.S. has been widely cited by  groups  and  publications  across the political spectrum, including by a  number of those  that  disagree with its positions .

These estimates from Guttmacher and the CDC are results of multiyear efforts to collect data on abortion across the U.S. Last year, Guttmacher also began publishing less precise estimates every few months , based on a much smaller sample of providers.

The figures reported by these organizations include only legal induced abortions conducted by clinics, hospitals or physicians’ offices, or those that make use of abortion pills dispensed from certified facilities such as clinics or physicians’ offices. They do not account for the use of abortion pills that were obtained  outside of clinical settings .

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The annual number of U.S. abortions rose for years after Roe v. Wade legalized the procedure in 1973, reaching its highest levels around the late 1980s and early 1990s, according to both the CDC and Guttmacher. Since then, abortions have generally decreased at what a CDC analysis called  “a slow yet steady pace.”

Guttmacher says the number of abortions occurring in the U.S. in 2020 was 40% lower than it was in 1991. According to the CDC, the number was 36% lower in 2021 than in 1991, looking just at the District of Columbia and the 46 states that reported both of those years.

(The corresponding line graph shows the long-term trend in the number of legal abortions reported by both organizations. To allow for consistent comparisons over time, the CDC figures in the chart have been adjusted to ensure that the same states are counted from one year to the next. Using that approach, the CDC figure for 2021 is 622,108 legal abortions.)

There have been occasional breaks in this long-term pattern of decline – during the middle of the first decade of the 2000s, and then again in the late 2010s. The CDC reported modest 1% and 2% increases in abortions in 2018 and 2019, and then, after a 2% decrease in 2020, a 5% increase in 2021. Guttmacher reported an 8% increase over the three-year period from 2017 to 2020.

As noted above, these figures do not include abortions that use pills obtained outside of clinical settings.

Guttmacher says that in 2020 there were 14.4 abortions in the U.S. per 1,000 women ages 15 to 44. Its data shows that the rate of abortions among women has generally been declining in the U.S. since 1981, when it reported there were 29.3 abortions per 1,000 women in that age range.

The CDC says that in 2021, there were 11.6 abortions in the U.S. per 1,000 women ages 15 to 44. (That figure excludes data from California, the District of Columbia, Maryland, New Hampshire and New Jersey.) Like Guttmacher’s data, the CDC’s figures also suggest a general decline in the abortion rate over time. In 1980, when the CDC reported on all 50 states and D.C., it said there were 25 abortions per 1,000 women ages 15 to 44.

That said, both Guttmacher and the CDC say there were slight increases in the rate of abortions during the late 2010s and early 2020s. Guttmacher says the abortion rate per 1,000 women ages 15 to 44 rose from 13.5 in 2017 to 14.4 in 2020. The CDC says it rose from 11.2 per 1,000 in 2017 to 11.4 in 2019, before falling back to 11.1 in 2020 and then rising again to 11.6 in 2021. (The CDC’s figures for those years exclude data from California, D.C., Maryland, New Hampshire and New Jersey.)

The CDC broadly divides abortions into two categories: surgical abortions and medication abortions, which involve pills. Since the Food and Drug Administration first approved abortion pills in 2000, their use has increased over time as a share of abortions nationally, according to both the CDC and Guttmacher.

The majority of abortions in the U.S. now involve pills, according to both the CDC and Guttmacher. The CDC says 56% of U.S. abortions in 2021 involved pills, up from 53% in 2020 and 44% in 2019. Its figures for 2021 include the District of Columbia and 44 states that provided this data; its figures for 2020 include D.C. and 44 states (though not all of the same states as in 2021), and its figures for 2019 include D.C. and 45 states.

Guttmacher, which measures this every three years, says 53% of U.S. abortions involved pills in 2020, up from 39% in 2017.

Two pills commonly used together for medication abortions are mifepristone, which, taken first, blocks hormones that support a pregnancy, and misoprostol, which then causes the uterus to empty. According to the FDA, medication abortions are safe  until 10 weeks into pregnancy.

Surgical abortions conducted  during the first trimester  of pregnancy typically use a suction process, while the relatively few surgical abortions that occur  during the second trimester  of a pregnancy typically use a process called dilation and evacuation, according to the UCLA School of Medicine.

In 2020, there were 1,603 facilities in the U.S. that provided abortions,  according to Guttmacher . This included 807 clinics, 530 hospitals and 266 physicians’ offices.

While clinics make up half of the facilities that provide abortions, they are the sites where the vast majority (96%) of abortions are administered, either through procedures or the distribution of pills, according to Guttmacher’s 2020 data. (This includes 54% of abortions that are administered at specialized abortion clinics and 43% at nonspecialized clinics.) Hospitals made up 33% of the facilities that provided abortions in 2020 but accounted for only 3% of abortions that year, while just 1% of abortions were conducted by physicians’ offices.

Looking just at clinics – that is, the total number of specialized abortion clinics and nonspecialized clinics in the U.S. – Guttmacher found the total virtually unchanged between 2017 (808 clinics) and 2020 (807 clinics). However, there were regional differences. In the Midwest, the number of clinics that provide abortions increased by 11% during those years, and in the West by 6%. The number of clinics  decreased  during those years by 9% in the Northeast and 3% in the South.

The total number of abortion providers has declined dramatically since the 1980s. In 1982, according to Guttmacher, there were 2,908 facilities providing abortions in the U.S., including 789 clinics, 1,405 hospitals and 714 physicians’ offices.

The CDC does not track the number of abortion providers.

In the District of Columbia and the 46 states that provided abortion and residency information to the CDC in 2021, 10.9% of all abortions were performed on women known to live outside the state where the abortion occurred – slightly higher than the percentage in 2020 (9.7%). That year, D.C. and 46 states (though not the same ones as in 2021) reported abortion and residency data. (The total number of abortions used in these calculations included figures for women with both known and unknown residential status.)

The share of reported abortions performed on women outside their state of residence was much higher before the 1973 Roe decision that stopped states from banning abortion. In 1972, 41% of all abortions in D.C. and the 20 states that provided this information to the CDC that year were performed on women outside their state of residence. In 1973, the corresponding figure was 21% in the District of Columbia and the 41 states that provided this information, and in 1974 it was 11% in D.C. and the 43 states that provided data.

In the District of Columbia and the 46 states that reported age data to  the CDC in 2021, the majority of women who had abortions (57%) were in their 20s, while about three-in-ten (31%) were in their 30s. Teens ages 13 to 19 accounted for 8% of those who had abortions, while women ages 40 to 44 accounted for about 4%.

The vast majority of women who had abortions in 2021 were unmarried (87%), while married women accounted for 13%, according to  the CDC , which had data on this from 37 states.

In the District of Columbia, New York City (but not the rest of New York) and the 31 states that reported racial and ethnic data on abortion to  the CDC , 42% of all women who had abortions in 2021 were non-Hispanic Black, while 30% were non-Hispanic White, 22% were Hispanic and 6% were of other races.

Looking at abortion rates among those ages 15 to 44, there were 28.6 abortions per 1,000 non-Hispanic Black women in 2021; 12.3 abortions per 1,000 Hispanic women; 6.4 abortions per 1,000 non-Hispanic White women; and 9.2 abortions per 1,000 women of other races, the  CDC reported  from those same 31 states, D.C. and New York City.

For 57% of U.S. women who had induced abortions in 2021, it was the first time they had ever had one,  according to the CDC.  For nearly a quarter (24%), it was their second abortion. For 11% of women who had an abortion that year, it was their third, and for 8% it was their fourth or more. These CDC figures include data from 41 states and New York City, but not the rest of New York.

Nearly four-in-ten women who had abortions in 2021 (39%) had no previous live births at the time they had an abortion,  according to the CDC . Almost a quarter (24%) of women who had abortions in 2021 had one previous live birth, 20% had two previous live births, 10% had three, and 7% had four or more previous live births. These CDC figures include data from 41 states and New York City, but not the rest of New York.

The vast majority of abortions occur during the first trimester of a pregnancy. In 2021, 93% of abortions occurred during the first trimester – that is, at or before 13 weeks of gestation,  according to the CDC . An additional 6% occurred between 14 and 20 weeks of pregnancy, and about 1% were performed at 21 weeks or more of gestation. These CDC figures include data from 40 states and New York City, but not the rest of New York.

About 2% of all abortions in the U.S. involve some type of complication for the woman , according to an article in StatPearls, an online health care resource. “Most complications are considered minor such as pain, bleeding, infection and post-anesthesia complications,” according to the article.

The CDC calculates  case-fatality rates for women from induced abortions – that is, how many women die from abortion-related complications, for every 100,000 legal abortions that occur in the U.S .  The rate was lowest during the most recent period examined by the agency (2013 to 2020), when there were 0.45 deaths to women per 100,000 legal induced abortions. The case-fatality rate reported by the CDC was highest during the first period examined by the agency (1973 to 1977), when it was 2.09 deaths to women per 100,000 legal induced abortions. During the five-year periods in between, the figure ranged from 0.52 (from 1993 to 1997) to 0.78 (from 1978 to 1982).

The CDC calculates death rates by five-year and seven-year periods because of year-to-year fluctuation in the numbers and due to the relatively low number of women who die from legal induced abortions.

In 2020, the last year for which the CDC has information , six women in the U.S. died due to complications from induced abortions. Four women died in this way in 2019, two in 2018, and three in 2017. (These deaths all followed legal abortions.) Since 1990, the annual number of deaths among women due to legal induced abortion has ranged from two to 12.

The annual number of reported deaths from induced abortions (legal and illegal) tended to be higher in the 1980s, when it ranged from nine to 16, and from 1972 to 1979, when it ranged from 13 to 63. One driver of the decline was the drop in deaths from illegal abortions. There were 39 deaths from illegal abortions in 1972, the last full year before Roe v. Wade. The total fell to 19 in 1973 and to single digits or zero every year after that. (The number of deaths from legal abortions has also declined since then, though with some slight variation over time.)

The number of deaths from induced abortions was considerably higher in the 1960s than afterward. For instance, there were 119 deaths from induced abortions in  1963  and 99 in  1965 , according to reports by the then-U.S. Department of Health, Education and Welfare, a precursor to the Department of Health and Human Services. The CDC is a division of Health and Human Services.

Note: This is an update of a post originally published May 27, 2022, and first updated June 24, 2022.

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Key facts about the abortion debate in America

Public opinion on abortion, three-in-ten or more democrats and republicans don’t agree with their party on abortion, partisanship a bigger factor than geography in views of abortion access locally, do state laws on abortion reflect public opinion, most popular.

About Pew Research Center Pew Research Center is a nonpartisan fact tank that informs the public about the issues, attitudes and trends shaping the world. It conducts public opinion polling, demographic research, media content analysis and other empirical social science research. Pew Research Center does not take policy positions. It is a subsidiary of The Pew Charitable Trusts .

Money Report

Moderna says new Covid vaccine showed stronger immune response than current shot in study

By annika kim constantino,cnbc • published march 26, 2024 • updated on march 26, 2024 at 12:16 pm.

• Moderna said a new version of its Covid vaccine triggered a stronger immune response against the virus than its current shot on the market in a late-stage trial. 
• The results come as Moderna competes with rival Pfizer for more share of the Covid vaccine market and tries to diversify its revenue streams after the steep drop in demand for Covid products last year.
• The biotech company's new "next-generation" shot offers the potential of a longer shelf life and is one component of its combination vaccine targeting Covid and the flu.

Moderna on Tuesday said a new version of its Covid vaccine triggered a stronger immune response against the virus than its current shot in a late-stage trial. 

The results come as Moderna competes with rival Pfizer for more share of the Covid vaccine market and tries to diversify its revenue streams after the world saw a plunge in demand for Covid products last year. Moderna's current Covid vaccine, known as Spikevax, is its only commercially available product. 

The biotech company's new shot could offer a longer shelf life and easier storage than its Covid vaccine. 

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Moderna's new shot is designed to last longer when refrigerated. That could make the jab easier to distribute around the world, especially in developing countries that may not have freezer capabilities. The company will accomplish that by shortening the length of the mRNA strand in the vaccine, Moderna previously told CNBC. 

The new shot is also a "critical component" of Moderna's combination vaccine targeting Covid and the flu, the company said in a release. Both Moderna and Pfizer have said that the convenience of receiving protection against two viruses at once could encourage more people to get vaccinated against Covid. 

The phase three trial followed roughly 11,400 people ages 12 and older in the U.S., U.K. and Canada. 

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Moderna's new shot specifically triggered a higher immune response against omicron subvariants BA.4 and BA.5 and the original strain of the virus than the company's bivalent vaccine targeting those variants. The benefits were "most acutely" seen in patients over the age of 65, who are also at highest risk of severe illness from Covid. 

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The most common side effects were injection site pain, headache, fatigue, muscle aches and chills, according to the company's release. Overall, Moderna said the safety profile is similar to the approved vaccine Spikevax. 

A detailed analysis of the late-stage trial results will be presented at Moderna's vaccines event for investors Wednesday. At the event, the company will highlight other parts of its pipeline. 

Moderna is working to develop shots against the flu, cancer and other disease. The company's shot against respiratory syncytial virus is expected to win Food and Drug Administration approval in May.

Moderna has also said it plans to launch up to 15 products in the next five years — a goal it first outlined during its annual research and development day in September.

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Academics challenge Florida law restricting research exchanges from prohibited countries like China

Two graduate students from China whose studies were put on hold, and a professor who says he is unable to recruit research assistants, are suing Florida education officials

MIAMI -- Two graduate students from China whose studies were put on hold, and a professor who says he is unable to recruit research assistants, sued Florida education officials on Monday, trying to stop enforcement of a new state law which limits research exchanges between state universities and academics from seven prohibited countries.

The law passed last year by the Republican-controlled Florida Legislature and signed by Gov. Ron DeSantis was designed to stop the Chinese Communist government and others from influencing the state’s public colleges and universities. The countries on the prohibited list are China, Russia, Iran, North Korea, Cuba, Syria, and Venezuela.

The law is discriminatory, unconstitutional and reminiscent of the Chinese Exclusion Act of 1882, which instituted a 10-year ban on Chinese laborers immigrating to the United States, according to the lawsuit filed in federal court in Miami.

The new law also usurps the power of the federal government, which has exclusive authority over immigration , national security and foreign affairs, the lawsuit said.

The law has forced two of the plaintiffs who are from China to put their graduate studies at Florida International University on hold and denied them entry into their research labs. The University of Florida professor who also is originally from China said the law has stopped him from recruiting the most qualified postdoctoral candidates to assist with his research, which has slowed his publishing productivity and research projects, according to the lawsuit.

In their lawsuit, the plaintiffs said they aren't members of the Chinese government nor the Communist Party.

According to the law, international students from the prohibited countries can be hired on a case-by-case basis with approval from the Board of Governors which oversees state universities or the state Board of Education, but the lawsuit said the law's “vagueness and lack of adequate guidance empowers and encourages arbitrary and discriminatory enforcement across Florida.”

The law “is having and will have far-reaching stigmatizing effects against individuals from China and of Asian descent who are seeking academic employment in Florida public universities and colleges, including plaintiffs, as Florida law now presumptively deems them a danger to the United States,” the lawsuit said.

The governor's office and the state Department of Education didn't respond to emails seeking comment.

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