Which of the following is true about independent variables?

Independent variables are crucial elements in experimental research as they are the factors that are intentionally manipulated by the researcher to assess their effect on other variables, typically the dependent variables. By altering the independent variable, researchers can observe how these changes influence outcomes, allowing them to establish cause-and-effect relationships. This manipulation is fundamental to the research design, enabling the identification of potential effects on the dependent variables, which are the outcomes measured during the experiment.

In contrast, the other options describe characteristics that do not accurately reflect the role of independent variables. For instance, independent variables are not the outcomes measured in the study, as that definition applies to dependent variables. Additionally, while independent variables may sometimes be constant during an experiment, they are generally varied to investigate their effects. Finally, independent variables are typically directly related to the research hypothesis, as researchers formulate hypotheses based on their expectations regarding how changes in the independent variable will influence the dependent variable.