# What is an Independent Variable? - Definition & Explanation

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Lesson Transcript
Instructor: Wind Goodfriend

Wind has her PhD in Social Psychology and Master's in Social Psychology from Purdue University.

The independent variable in an experiment is what the experimenter controls to create two or more comparison groups. Learn more about independent variables through several examples and test your knowledge with quiz questions.

## Definition of an Independent Variable

Imagine you and your friend sign up to participate in a psychology research study. When you arrive, you go into one room and your friend goes into another. You watch a horror movie (let's say Dracula) while your friend watches a comedy (let's say Monty Python's Life of Brian). During the movie, you're allowed to eat as much popcorn as you want. The experimenters believe that people who watch comedies eat more popcorn compared to people who watch horror movies. In any experiment, different groups are compared on the outcome (like popcorn eaten), which is called the dependent variable. Whatever makes the two groups different from each other is called the independent variable.

## How Independent Variables Work in an Experiment

In the example above, the difference between the two groups in the experiment was what movie people watched. So here, the independent variable is type of movie. The independent variable in an experiment will always be identified using three rules:

• First, the independent variable is what the experimenters set up in advance to make two or more groups that are different from each other. Here, the two rooms were set up to show different movies.
• Second, always what happens first before the outcome is measured. People watched a movie first, then the amount of popcorn they ate was measured at the end.
• Finally, considered the cause of any changes in the dependent variable. Here, different types of movies were considered the cause of any differences in amount of popcorn eaten. The amount of popcorn is considered dependent on which movie was watched.

## More Examples

We've gone through one example already; we said that the type of movie watched might have an effect on the amount of popcorn eaten. In this example, the independent variable is the type of movie, while the dependent variable was the amount of popcorn eaten. What are some other examples?

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