Pretest-Posttest Design: Definition & Example

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  • 0:07 Definition
  • 1:38 Example 1
  • 4:00 Example 2
  • 5:35 Lesson Summary
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Lesson Transcript
Instructor
Devin Kowalczyk

Devin has taught psychology and has a master's degree in clinical forensic psychology. He is working on his PhD.

Expert Contributor
Jennifer Levitas

Jennifer has a Ph.D. in Psychology. She's taught multiple college-level psychology courses and been published in several academic journals.

This lesson explores the process and technique of using a pretest-posttest design in psychology. Two simple examples will allow you to understand how to apply this type of design in a future experiment.

Definition

You've probably got some ideas of how experiments should be run. Why don't researchers just look at something, poke it with a stick, and then study the changes? Researchers are always making things super complicated.

I am glad to inform you that there is a methodology very similar to this, most of the time occurring without the stick. A pretest-posttest design is usually a quasi-experiment where participants are studied before and after the experimental manipulation. Remember, quasi-experimental simply means participants are not randomly assigned. It is possible to have a control group, or a group who doesn't receive the manipulation, but we will not be looking at that in this lesson. In a pretest-posttest design, there is only one group and all of them are in the experimental condition.

The reason you run a pretest-posttest experiment is to see if your manipulation, the thing you're looking at, has caused a change in the participants. Since everyone is being manipulated in the same way, any changes you see across the group of participants is likely from the manipulation. This means you test them before doing the experiment, then you run your experimental manipulation, and then you test them again to see if there are any changes. So how does this really work?

Example 1

Have you ever tried to go about your day when you haven't showered, brushed your teeth, or really cleaned yourself? Let's say you're a researcher who is interested in how much the feeling of being unclean affects judgment and general knowledge. You settle on a pretest-posttest design. You will administer a pretest on general knowledge and judgment, then have your experimental manipulation of the participants not cleaning themselves, then perform a posttest using the same or similar tests.

You collect your participants and give them a series of tests that will measure their judgment and general knowledge. For example, you may look at their ability to discern when it would be a good time to pull out into traffic as a measure of judgment. For general knowledge, you write up a short test about historical, scientific, and literary ideas.

Next, you instruct all of your participants to not shower, brush their teeth, or clean themselves for 36 hours. This is to ensure maximum nasty grossness in your study. After 36 hours, your participants return.

You likely would not give them the exact same tests because there's a practice effect, defined as an influence on performance from previous experience. So if you have them do the exact same car driving sequence, they may have learned a pattern or become familiar with the machine. If you give them the exact same general knowledge test, then they may have looked up some of the answers or had a chance to remember more.

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Additional Activities

Pretest-Posttest Design

Activity 1:

For this activity, imagine that you are a research psychologist. You believe that the development of resilience in childhood is essential to optimal development. You know that there is a biological component to resilience in that some children are born more resilient than others, but also believe that resilience can be taught. You develop an intervention to teach resilience to middle school students. Write two to three paragraphs explaining how you would implement a pretest-posttest design, and why it would be necessary for this study. For example, since people start with different levels of resilience, you may opine that it is important to measure the beginning level of this construct with a pretest You then may want to examine whether the level of resilience has changed using a posttest.

Activity 2:

Imagine that you have a professional research colleague who believes that drinking orange juice increases intelligence. He uses a pretest-posttest design to test his theory. He gives a group of students an IQ test (a pretest) and tells them to drink one glass of orange juice with dinner that night and one glass with breakfast the next morning. The next day they take another IQ test (a posttest) and incredibly the IQ scores are higher. He believes he has discovered something momentous, but you know that there is something wrong with his pretest-posttest design. Write one to two paragraphs describing why this study is flawed (hint: do you think that practice effects could have played a role in invalidating this experiment?).

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