Limits to Generalization of a Research Study

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  • 0:07 Purpose of Research
  • 1:21 Representativeness
  • 3:13 Replicability
  • 4:49 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.

What happens if a research study confirms the researcher's hypothesis? In this lesson, we'll look at the limits of generalizing from a single research study, including the importance of representativeness and replicability.

Purpose of Research

Sydney is a psychologist. She's interested in studying the impact of an intervention on the bullying rate in a middle school. She wants to see if the intervention that she has designed will decrease middle school bullying. If so, it could be a great thing for middle schools everywhere!

So, Sydney goes to a middle school class and measures how much bullying goes on there. Then she does her intervention on the class and measures how much bullying occurs afterward. She finds that there is significantly less bullying after her intervention than before.

That's great! That means that Sydney's intervention lowers bullying rates in middle school students, right? Middle schools everywhere can adopt her intervention, and bullying will be lowered across the board.

The purpose of research is to make statements about something that occurs in the real world. In Sydney's example, she did research on one class in one middle school in one town in the entire country. But she's not interested only in what happened in that class; she wants to be able to say that this intervention will lower the bullying rate of middle schools everywhere. Let's look closer at the problems that might arise when trying to draw conclusions from only one study.


Remember that Sydney found that her intervention lowered the amount of bullying in a middle school class. She believes that the intervention will work universally. That is, she believes that if every middle school student is exposed to her intervention, bullying rates will be lowered across the nation.

This might be true, but can she say that based on her one study? Maybe not. One key element to being able to generalize results is to have a representative sample, or a group of subjects that will behave in the same way as the population. Think about it like this: you want the people in your study to represent the population, which is why it is called a 'representative sample.'

It is possible, but very, very difficult, to have a representative sample in only one study. For example, what if the students in the class that Sydney studied are just more predisposed to being affected by her intervention? Or what if something happened, like a classmate getting seriously hurt by a bully, that means that they are ready to change their behaviors for the better?

Even if Sydney did her study using many students at many different schools, she might not have a representative population. For example, perhaps all of her subjects are the same race or class or perhaps they are all from the country instead of the city. Will her results translate to other races, classes or geographic areas? Perhaps, but perhaps not. It's very hard to tell from only one study.

However, if Sydney or someone else did the same study but with middle schoolers from another part of the country, another class and/or another race, their results together might begin to make up a representative sample. This is one reason why the same research might be done over and over on different samples.

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