In psychological research, what is defined as a deliberately manipulated variable?

The correct choice is the independent variable, which is indeed defined as the deliberately manipulated variable in psychological research. Researchers manipulate the independent variable to observe its effects on other variables, specifically the dependent variable. This manipulation is essential for establishing a cause-and-effect relationship within an experiment.

In a typical experiment, the independent variable comes first, and researchers vary it to see how these changes influence the outcomes measured in the study, namely the dependent variable. For instance, if a psychologist is studying the impact of different levels of stress on performance, the level of stress would be the independent variable, as it is manipulated by the researcher to assess its effects on performance outcomes.

Understanding the distinction between the independent variable and other variables is crucial. The dependent variable represents the outcome that is measured and is dependent on the manipulation of the independent variable. Controlled variables are factors kept constant to ensure that the results are due to the manipulation of the independent variable, while confounding variables are external factors that might influence the dependent variable, potentially skewing results if not controlled for.