In a research study, which term describes the variable that the researcher actively changes?

• A. The variable being measured (outcome)
• B. The variable being manipulated by the researcher
• C. A variable controlled for but not of interest
• D. The sample size

Answer: (B)

The key idea here is identifying the independent variable—the one the researcher actively changes in an experiment to see its effect on the outcome. When you manipulate something on purpose, you’re testing how that change influences what you measure.

So the best choice describes the variable the researcher controls, the one you set at different levels or conditions to observe how the dependent variable responds. The variable being measured is the outcome you assess, not the one you change. A variable controlled for but not of interest is kept constant to reduce confounding, not to explore its effect. And sample size is a study parameter, not a variable you manipulate or measure as part of the causal analysis.

For example, if you’re examining how caffeine affects reaction time, caffeine administration is the manipulated (independent) variable, and reaction time is the measured (dependent) outcome.