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.
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).
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).Within-group differences often come to light when a researcher is conducting a between-group research study.
For example, there are many studies that talk about the differences between boys and girls. These might point out, for example, that one group does better on math tests, or that the two genders communicate differently, or even that there are differences in the brains of boys and girls. These are all between-group studies.
However, when you look closely at these studies, you might see something interesting. The within-group differences are often greater than the between-group differences. To understand what this means, let’s go back to Lorinda’s study on gender and the math test.Let’s say that the mean score for boys on the math test is 87, and the mean score for girls is 93.
Sounds like there’s a difference in the genders, right? But what if the scores for the girls ranged from 76 to 100, while the scores for the boys ranged from 80 to 97? In that case, the within-group differences (24 points for girls and 17 points for boys) are much larger than the difference in the mean scores between the two genders (6 points).Does this mean that girls are better at math than boys are? Looking at the between-group differences, you might think so. And you might be right.
But when you look at the variation within groups, you might see that there doesn’t appear to be much of a difference between boys and girls after all. In fact, if you compared two girls’ scores, you might find that their scores are more different than if you compared a boy and a girl. Within-group differences do not always contradict or cancel out between-group differences, but they can help paint a fuller picture of what’s going on.
Every social science research study has one or more groups of subjects, or sets of participants who are being studied.
There are two ways to look at the data about these groups. Between-group differences show how two or more groups are different, whereas within-group differences show differences among subjects who are in the same group. Within-group differences can come to light when looking at a between-group research study. While within-group differences do not always contradict or cancel out between-group differences, they can help paint a fuller picture of what’s going on.