Subject variables, also known as independent variables, are the key elements in an experiment or study that are intentionally manipulated or controlled by the researcher. They are the characteristics, conditions, or factors that are hypothesized to have an effect on the dependent variable.

Subject variables play a crucial role in research as they allow researchers to investigate the relationship between the independent variable(s) and the dependent variable(s) of interest. By systematically varying the subject variables, researchers can assess the impact or influence they have on the outcome or behavior being measured.