Extraneous & Confounding Variables: Differences & Examples

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  • 0:06 Internal Validity
  • 1:45 Extraneous Variables
  • 4:21 Confounding Variables
  • 6:00 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.

What happens when something other than your independent variable is influencing the outcome of your study? In this lesson, we'll look at two types of variables that can affect an experiment: extraneous and confounding variables.

Internal Validity

Josh is in love. He's been with his girlfriend a while now and wants to propose. But he doesn't know how he should do it. Should he propose in a crowd? When they're alone? At the place where they went for their first date? After he whisks her off to Paris or the Bahamas?

Josh is a psychologist and does research for a living, so he decides to do a study on marriage proposals and figure out which one women like best. That's how he'll decide how to propose. He gathers a bunch of women, shows them videos of marriage proposals, and then measures their reactions: whether they cry or if their heart races or if they just watch it and go, 'Eh.'

In research, internal validity is when a researcher can say that only the independent variable caused changes in the dependent variable. For example, in Josh's study, the videos are the independent variable and the women's reactions are the dependent variable. If Josh changes which videos he shows the women, he sees different reactions. If his internal validity is high, he can say that the difference in videos caused the changes in the reactions.

If most women who watch video A say, 'Aw, how sweet!' and most women watching video B say, 'Well, that's an epic fail,' then Josh wants to know for sure that it's actually the video that's causing the reactions, not something else. Let's look closer at variables that might affect the dependent variable besides the independent variable: extraneous and confounding.

Extraneous Variables

Okay. So, let's imagine that Josh has set up his experiment. Each subject is brought into a little room and is shown two of six different videos. Josh measures their reaction to each video and then their reaction overall.

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