Matched-Group Design: Definition & Examples

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  • 0:08 Experimental Design
  • 1:25 Equivalent Groups
  • 4:12 Strengths and Limitations
  • 5:46 Lesson Summary
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Lesson Transcript
Instructor: Natalie Boyd

Natalie is a teacher and holds an MA in English Education and is in progress on her PhD in psychology.

Choosing how to divide subjects into groups is a major part of experimental design. In this lesson, we'll look at a type of non-random assignment, matched-group design, and its strengths and limitations.

Experimental Design

Daphne is a psychologist, and she wants to know whether the type of music a person listens to while studying will impact how well they learn math. Daphne believes that classical music will lead to better learning than rock music. But how does she find out if she's right? What should she do?

Experimental design is the process of making decisions about how to run an experiment to answer a question. Essentially, experimental design is where a researcher decides how to actually find an answer to their research question. For example, Daphne wants to know if classical music will lead to better learning than rock music. She enlists volunteers and has half of them listen to rock music while studying and has the other half listen to classical music while studying.

Afterward, she gives them all a math test to see how well they do. If she's right, the scores on the math test should be higher for the people listening to classical music versus the people listening to rock music. Every element of Daphne's study, from gathering subjects to giving them the math test, is part of experimental design. Let's look closer at one type of design that can make studies like Daphne's stronger: matched-subjects design.

Equivalent Groups

So Daphne has her two groups of subjects: the classical music subjects and the rock music subjects. And when she gets her results back, she realizes that her classical music subjects did better on the math exam than the rock music group did. Her study has supported her hypothesis, so that's it, right?

Not so fast. You see, there's a problem. It turns out that the subjects in the classical music group have taken more math classes than the subjects in the rock music group. They're better at math, so how does she know that it was the music and not their knowledge of math that made them score better on the test? The answer is, she can't know.

How could Daphne's groups end up so unequal? There are a couple of ways that Daphne could have assigned people to the groups. If she purposely chose to put people who have a lot of experience in math into the classical music group, that's an example of experimenter bias or researcher error.

Usually, to get around bias and error in assigning groups, researchers opt to do random assignment; that is, they randomly choose who goes into what group, like by flipping a coin. But chance could lead to Daphne's problem even if she randomly assigned her subjects. Because of that, sometimes researchers choose to do a matched-subjects design, or matched-group design, which is an experiment where the subjects are matched based on a particular variable and then put into groups. By matching subjects, the researcher is creating equivalent groups for their study.

Matching is almost always done by looking at a variable that could affect the dependent variable. In Daphne's study, the dependent variable is scores on the math test. She might want to match people based on their age (since older students will have had more math classes), major (since math majors will presumably score higher than English majors), IQ, or another measure.

Remember when you were a kid and had to split up a pile of something, like candy? You'd pass one to the other person and say, 'One for you.' Then you'd put one into your own pile and say, 'One for me.' You'd keep doing that until all the candy was passed out.

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