Which description correctly defines the independent variable in an experiment?

• A. It is measured after the experiment.
• B. It remains constant across all setups.
• C. It is the outcome measured by the observer.
• D. It is the variable deliberately changed to test its effect.

Answer: (D)

The independent variable is the factor you deliberately change to test its effect on the outcome. In an experiment, you set and vary this variable to see how it influences what you measure. For example, if you’re studying how sunlight affects plant growth, the amount of sunlight is the independent variable because you actively change it to observe the result. The thing you measure, like plant height or biomass, is the dependent variable—it depends on the amount of sunlight. The option that says it’s measured after the experiment describes the dependent variable, not the independent one, and the option that says it remains constant describes a controlled variable, which you keep the same to avoid affecting results. The correct description is the one that identifies the independent variable as the factor you deliberately change to test its effect.