What defines an independent variable in an experiment?

In an experiment, the independent variable is defined as the variable that is actively manipulated by the researcher to investigate its effects on other variables. This manipulation allows the researcher to establish a cause-and-effect relationship between the independent variable and the dependent variable, which is the outcome being measured. By changing the independent variable, the researcher can observe how those changes lead to outcomes in the dependent variable, thus providing insights into the relationship between the two.

In contrast, the other options describe different roles within the experimental framework. The outcome measured corresponds to the dependent variable, not the independent variable. A variable kept constant throughout the study is referred to as a control variable or constant, essential for eliminating confounding factors but not the independent variable itself. Lastly, a variable that influences the independent variable does not fit the definition; rather, it could be an extraneous variable or a moderator but is not what defines the function of an independent variable. Understanding the role of the independent variable is crucial for designing and interpreting experiments effectively.