Methods for Increasing External Validity

Methods for Increasing External Validity
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  • 0:07 External Validity
  • 1:12 Aggregation
  • 2:36 Nonreactive Measures
  • 3:49 Field Research
  • 5:00 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.

External validity is a key component of research. In this lesson, we'll look at several different ways to increase external validity, including aggregation, nonreactive measures, and field research.

External Validity

Candace is a psychologist who is interested in studying if people act differently when they are alone versus when they are with other people. She asks for volunteers for her study. When they show up for the study, she tells them that she's not ready yet and asks them to wait in a room.

In the room is a bowl of candy that has a sign on it that says, 'Take only one, please.' Some of the subjects are left completely alone in the room, while others are left in the room with someone else. Secretly, Candace watches from another room to see how many candies people take. She believes that the people alone in the room will take more than one candy.

Candace's study is very specific, but like other researchers, Candace wants to generalize her findings to tell her something about life beyond her experiment. External validity is the extent to which the results of a study can be generalized to the world at large. Let's look at some ways that researchers can increase the external validity of their studies so that they can generalize their findings.


Candace, like many psychologists, works and does research at a university. The only volunteers she can get to participate in her study are college students. But is their behavior the same as the behavior of middle-aged people? What about elementary school children? Or people who do not have the resources to go to college?

One threat to the external validity of Candace's study is the fact that her sample (or group of participants) might not represent the entire population. So what should she do? Should she just throw out the results of her study?

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