The purpose of research is to say something about the real world. But how can a researcher generalize results to the world at large? In this lesson, we’ll answer that question as we learn about external validity.

External Validity

Sarah is a psychologist who teaches and does research at an expensive, private college. She’s interested in studying whether offering specific praise after a task will boost people’s self-esteem. If her hypothesis is correct, then giving someone a specific compliment on a job well done after a task will make them feel better about themselves. And, if she can show that specific praise post-task boosts self-esteem, then managers at companies everywhere will be able to boost their employees’ self-esteem by offering them specific praise.

But, here’s a problem: the volunteers that Sarah gets for her study are all college students, most of them are white, and most of them are from privileged backgrounds. Sarah worries that her results might not be applicable to people who are not in their late teens or early 20s, white, and rich.

External validity is the extent to which results of a study can be generalized to the world at large. Sarah is worried that her study might have low external validity. Let’s look closer at external validity, including why it’s important and the balance between control and generalization that is required for external validity.


Let’s go back to Sarah’s concerns about her study for a moment. She’s worried because all of her subjects are similar to each other, and they represent only a very small portion of the population. If Sarah’s study shows, for example, that specific praise after a task boosts self-esteem, what does that mean for the real world?

If all of Sarah’s subjects are young, white, and upper-class, can she know for sure that this specific praise after a task will boost the self-esteem of an older, minority, lower-class worker?

The goal of research is to generalize to the world at large. Perhaps, like Sarah, the goal is to generalize to the population as a whole, based on an experiment done on a small sample of the population. Or, perhaps the goal is to generalize from a task done in a lab to a real-world setting, like an office or a school. Either way, the goal is to make inferences about the way things work in the real world based on the results of a study.

But, without external validity, a researcher cannot make those inferences. If external validity is low on a study, the results won’t translate well to other conditions. That means that the research done doesn’t tell us anything about the world outside of the study. That’s a very limited viewpoint!

Control vs. Generalization

OK, you might be thinking, so just make sure that every study has a whole lot of external validity. What’s the big deal?

Well, that’s easier said than done. There’s a balance in research between control and generalization. Essentially, the problem is this: with a study in a lab, there is low external validity. That is, it isn’t always applicable to the real world.

The other option is to do research in the field – that is, to conduct research in the real world. Sarah, for example, could go to an office or a factory and do her experiment there with real workers and managers. Then, she’d have a very high external validity.

But, you can’t control things in the real world the way you can in the lab, so other variables might come into play. This weakens internal validity, or the extent to which a researcher can say that only the independent variable is causing the dependent variable.

So on one hand, you can research in a lab and have a lot of control over the variables and a strong argument that only your independent variable matters. On the other hand, you could do research in the field and have a strong relationship to the real world and generalizing results.

There are always payoffs in research, and every study has to find the right balance between internal and external validity, or control and generalization. What that balance is depends on the goals of the researcher and the study itself.

Lesson Summary

External validity is the extent to which results of a study can be generalized to the world at large. Because the goal of research is to tell us about the world, external validity is a very important part of designing a study. But, there’s also a balance that needs to be struck between having control over your variables and being able to generalize results. This tension is also known as the tension between internal and external validity.

Learning Outcomes

After you’ve completed this lesson, you should be able to:

  • Define external validity
  • Explain the importance of external validity in research studies
  • Discuss the need to balance control and generalization when performing research