Which variable is manipulated to observe its effect on another variable?

The independent variable is the factor that is manipulated by the researcher to examine its effect on another variable, known as the dependent variable. By changing the level or presence of the independent variable, researchers can observe any resulting changes in the dependent variable. This is foundational in experimental design because it helps establish cause-and-effect relationships.

In a controlled experiment, the manipulation must be systematic and may include factors such as dosage of a treatment, type of intervention, or conditions under which behavior is measured. The ability to isolate the independent variable allows researchers to draw conclusions about its impact on the outcome, providing clear evidence for the hypotheses being tested.

Understanding the role of the independent variable is crucial for effective research design, as it directly influences the conclusions that can be drawn from the study.