What Is the Independent Variable?

Researcher manipulating independent variables.
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The independent variable is the characteristic of a psychology experiment that is manipulated or changed. For example, in an experiment looking at the effects of studying on test scores, studying would be the independent variable. Researchers are trying to determine if changes to the independent variable (studying) result in significant changes to the dependent variable (the test results).

Observations About the Independent Variable

"Why is the independent variable labeled the independent variable?

Because it is independent of research participants' actions - participants have no control over what condition or group they are assigned to. It is the experimenter who manipulates the independent variable, whereas participants have nothing to do with it (they are simply exposed to one version of the independent variable)."
(Breckler, Olson, & Wiggins, 2006)

"Independent variables are selected because an experimenter believes they will cause changes in behavior. Increasing the intensity of a tone should increase the speed at which people respond to the tone. Increasing the number of pellets given to a rat for pressing a bar should increase the number of times the bar is pressed. When a change in the level (amount) of an independent variable causes a change in behavior, we say that the behavior is under the control of the independent variable."
(Kantowitz, Roediger, & Elmes, 2009)

"It is crucial that the experimental and control groups in a study be very similar, except for the different treatment that they receive in regard to the independent variable.

This stipulation brings us to the logic that underlies the experimental method. If the two groups are alike in all respects except for the variation created by the manipulation of the independent variable, then any differences between the two groups on the dependent variable must be due to the manipulation of the independent variable.

"
(Weiten, 2013)

Examples of Independent Variables

  • A researcher wants to determine if the color of an office has any effect on worker productivity. In an experiment, one group performs a task in a yellow room while another performs the same task in a blue room. In this example, the color of the office is the independent variable.
  • Researchers want to learn whether listening to fast-paced music helps runners perform better during a marathon. In an experiment, one group of runners listens to fast-paced music while another group listens to slow-paced music. In this example, the type of music the runners listen to is the independent variable.
  • A business wants to determine if giving employees more control over how to do their work leads to increased job satisfaction. In an experiment, one group of workers is given a great deal of input in how they perform their work, while the other group is not. The amount of input the workers have over their work is the independent variable in this example.
  • Educators are interested in whether participating in after-school math tutoring can increase scores on standardized math exams. In an experiment, one group of students attends an after-school tutoring session twice a week while another group of students does not receive this additional assistance. In this case, participation in an after-school math tutoring is the independent variable.
  • Researchers want to determine if a new type of treatment will lead to a reduction in anxiety for patients suffering from social phobia. In an experiment, some volunteers receive the new treatment, another group receives a different treatment, and a third group receives no treatment. The independent variable in this example is the type of therapy.

Sources

Breckler, S., Olson, J., & Wiggins, E. (2006). Social psychology alive. Belmont, CA: Wadsworth.

Kantowitz, B. H., Roediger, H. L., & Elmes, D. G. (2009). Experimental psychology. Belmont, CA: Wadsworth.

Weiten, W. (2013). Psychology: Themes and variations, 9th ed. Belmont, CA: Wadsworth.

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