What distinguishes an independent variable from a dependent variable?

The distinction between independent and dependent variables is fundamental in psychological research. The independent variable is the one that the researcher manipulates or changes to observe its effects on other variables. In contrast, the dependent variable is what is measured in the experiment. This means that the dependent variable is expected to change when the independent variable is altered.

In this context, option B accurately captures the essence of this relationship: the independent variable is indeed changed by the researcher, while the dependent variable is measured to determine the effect of that change. By manipulating the independent variable, researchers can infer causal relationships between the two variables, helping to establish how different factors influence behavior or outcomes.

The other options present misunderstandings of the terminology or relationship between these variables. For instance, option A inaccurately states that the independent variable is what is measured, which is actually the role of the dependent variable. Option C incorrectly suggests that both variables are manipulated, whereas only the independent variable is changed in a controlled experiment. Finally, option D limits the definition of an independent variable by asserting that it must be a physical measurement, which is not the case, as independent variables can also be categorical or qualitative in nature.