Which characteristic correctly defines an independent variable?

An independent variable is defined as the factor that is manipulated or controlled by the researcher in an experiment to observe its effects on the dependent variable. This characteristic is essential in establishing a cause-and-effect relationship. By changing the independent variable, researchers can determine if it has a significant impact on the outcome they are measuring, which is represented by the dependent variable. This manipulation is crucial for experimental design, allowing for controlled comparisons and increased internal validity of the study.

In contrast, the other characteristics provided do not accurately define an independent variable. While the dependent variable is typically influenced by changes in the independent variable, this does not describe the independent variable itself. Identifying the independent variable is part of the study's design phase and should be established before the study is completed. Finally, while some studies may keep certain variables constant to isolate the effects of the independent variable, the independent variable itself is specifically intended to be the one that is changed or manipulated throughout the study.