Independent Variable (IV) is defined as:

Independent Variable (IV) is defined as:

• A. The variable that is measured by the researcher.
• B. The variable kept constant throughout.
• C. An aspect of the experimental situation that is manipulated by the researcher or changes naturally so the effect on the DV can be measured.
• D. A random factor used to assign participants.

Answer: (C)

The independent variable is the factor you change to see if it affects the outcome. In experiments you deliberately manipulate this variable, and sometimes it can vary naturally across groups in quasi-experimental designs, so you can observe its effect on the measured outcome. This description fits best because it captures both ways the IV can operate: it's something you change (manipulated by the researcher) or something that varies naturally, with the aim of seeing how that variation influences the dependent variable. Think of an example: if you want to test whether caffeine affects reaction time, the amount of caffeine given to participants is the independent variable, while the reaction time you measure is the dependent variable. The other statements describe different things. The variable you measure (reaction time) is the dependent variable, not the IV. Keeping a variable constant is a control variable. A random factor used to assign participants refers to randomization or assignment procedures, not the manipulated variable.

The independent variable is the factor you change to see if it affects the outcome. In experiments you deliberately manipulate this variable, and sometimes it can vary naturally across groups in quasi-experimental designs, so you can observe its effect on the measured outcome.

This description fits best because it captures both ways the IV can operate: it's something you change (manipulated by the researcher) or something that varies naturally, with the aim of seeing how that variation influences the dependent variable.

Think of an example: if you want to test whether caffeine affects reaction time, the amount of caffeine given to participants is the independent variable, while the reaction time you measure is the dependent variable.

The other statements describe different things. The variable you measure (reaction time) is the dependent variable, not the IV. Keeping a variable constant is a control variable. A random factor used to assign participants refers to randomization or assignment procedures, not the manipulated variable.