Within-Group vs. Between-Group Research

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  • 0:04 Groups of Subjects
  • 0:44 Between-Group Differences
  • 1:53 Within-Group Differences
  • 4:23 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.

There are two ways to look at the differences between subjects in a research study, between-group and within-group differences. In this lesson, we'll discuss what each method is and how they differ from each other.

Groups of Subjects

Lorinda is doing a study. She thinks that girls will do better on a math test than boys will. So she gives the test to boys and girls and then grades the results to see which group does better.

Every social science research study has one or more groups of subjects, or sets of participants who are being studied. In Lorinda's case, she has two groups: girls and boys. But what happens if she discovers that there are more differences between two girls than there are between a boy and a girl?

To help Lorinda out, let's talk about within-group and between-group research.

Between-Group Differences

As we said, Lorinda is giving a math test to two groups, boys and girls, and she wants to see if there's a difference between the two groups. What she's looking for are between-group differences, or data that shows that two or more groups are different.

Between-group research is the most common type of research, and it can take many forms. In Lorinda's case, her groups are established already. That is, her subjects are already boys and girls, even before her study.

Sometimes, though, a researcher might create groups for their research. For example, if Lorinda wanted to test how well a math game helps students, she might create two groups: an experimental group, which plays the math game before taking the test, and a control group that does not play the math game before the test.

The number of groups can vary as well. For example, Lorinda is looking at two groups: boys and girls. But what if she wants to divide her subjects by age? She might have three or four groups if she's looking at different ages.

Whether the researcher creates the groups or they exist already, and regardless of whether there are two groups or more, between-group research focuses on the differences between the groups (hence its name).

Within-Group Differences

Like most researchers, Lorinda is looking for between-group differences, based on the average score on a math test. In other words, she wants to know if the mean score for girls is different from the mean score for boys.

But not every girl will perform equally on the test. There might be a lot of different scores when Lorinda looks at all the girls. When the data shows differences among subjects that are in the same group, this is known as within-group differences.

Within-group research can take a number of different forms. Often, a researcher only wants to look at one group; therefore, their research will only look at within-group differences. For example, if Lorinda only wanted to look at the scores of seven-year-old girls, and didn't want to compare them to any other group, she would look for trends and differences within that group of people (i.e., the seven-year-olds).

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