What is the role of the independent variable in an experiment?

• A. It is the outcome measured to determine the effect.
• B. It is the variable kept constant to prevent effects.
• C. It is deliberately manipulated to test its effect on the dependent variable.
• D. It is simply a participant characteristic used in sampling.

Answer: (C)

In experiments, the independent variable is the factor the researcher deliberately changes to see if it affects the outcome. By setting different levels of this variable (for example, different caffeine doses), you actively control what participants experience and observe whether the dependent variable—what you measure like reaction time—changes as a result. Keeping other variables constant helps ensure that any observed effect is due to the manipulation of the independent variable rather than other factors. The dependent variable is the measured outcome, while constants are things you hold steady to prevent confounding, and participant characteristics are potential variables you don’t manipulate to test a cause.