Which statement describes a control variable?

Which statement describes a control variable?

• A. A variable changed to observe response
• B. A variable that varies randomly
• C. A variable that is not measured
• D. A variable kept constant to isolate the effect of the independent variable

Answer: (D)

In experiments, you want to reveal how one factor affects another without interference from other influences. A control variable is kept constant across all conditions so it cannot affect the outcome, which helps isolate the effect of the independent variable. That’s why describing it as a variable kept constant to isolate the independent variable’s effect is the best fit. For example, in studying how sunlight affects plant growth, you would keep soil, pot size, and water consistent. The other ideas describe the thing you’re changing (the independent variable), random variation, or data you’re not measuring, none of which capture the role of a control variable.

In experiments, you want to reveal how one factor affects another without interference from other influences. A control variable is kept constant across all conditions so it cannot affect the outcome, which helps isolate the effect of the independent variable. That’s why describing it as a variable kept constant to isolate the independent variable’s effect is the best fit. For example, in studying how sunlight affects plant growth, you would keep soil, pot size, and water consistent. The other ideas describe the thing you’re changing (the independent variable), random variation, or data you’re not measuring, none of which capture the role of a control variable.