What is an independent variable in experimental research?

An independent variable in experimental research is defined as the variable that is manipulated by the researcher to observe its effect on another variable, known as the dependent variable. By changing or controlling this variable, researchers can analyze how these changes influence outcomes in the experiment. The manipulation is a key aspect, as it allows the experimenter to establish cause-and-effect relationships. For instance, in a study examining the impact of different teaching methods on student performance, the teaching method would be the independent variable because it is the factor being manipulated to see how it affects student outcomes.

The other options focus on variables that are either measured, controlled, or kept constant, which describes different roles in an experimental setup rather than the role of the independent variable itself. The independent variable's critical characteristic is its direct manipulation in the study, setting it apart from these other types of variables.