In an independent groups design, what does the experimental researcher manipulate?

In an independent groups design, the experimental researcher manipulates the independent variable. This is the variable that is intentionally changed or controlled in an experiment to test its effect on the dependent variable. By doing so, researchers can observe how variations in the independent variable influence outcomes measured by the dependent variable.

The independent variable is crucial for establishing cause-and-effect relationships within the study. For instance, if a researcher is testing the effects of a new teaching method on student performance, the teaching method represents the independent variable that would be varied among different groups of students.

In contrast, the dependent variable reflects the outcome being measured in response to the changes made in the independent variable. Extraneous variables can influence the results but are not the focus of manipulation; rather, they need to be controlled to ensure that any observed effects can be attributed to the independent variable. The controlled group is often a reference point or baseline in the experiment, used to compare the effects observed with experimental conditions but is not something the researcher manipulates directly like the independent variable.