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For example, consider a hypothetical experiment on the effect of drinking alcohol on reaction time: Subjects drank either water, one beer, three beers, or six beers and then had their reaction times to the onset of a stimulus measured. The independent variable would be the number of beers drunk (0, 1, 3, or 6) and the dependent variable would be reaction time.

Some variables (such as reaction time) are measured on a continuous scale. There is an infinite number of possible values these variables can take on. Other variables can only take on a limited number of values. For example, if a dependent variable were a subject's rating on a five- point scale where only the values 1, 2, 3, 4, and 5 were allowed, then only five possible values could occur. Such variables are called "discrete" variables.

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