In an experiment, which variable is deliberately changed to test its effect?

• A. The dependent variable
• B. The control variable
• C. Extraneous variable
• D. The independent variable

Answer: (D)

When you design an experiment, you deliberately change one factor to see what effect it has. That factor is the independent variable. You’re looking to see how altering it changes the outcome you measure. The thing you measure to see the effect is the dependent variable. To make sure the change you observe is due to the independent variable and not other factors, you keep other variables constant as control variables. Any other factors that could influence the result are extraneous variables, which you try to minimize or account for.

For example, if you want to know how fertilizer amount affects plant growth, the fertilizer amount is the independent variable, plant height or biomass is the dependent variable, and you would keep watering, light, soil type, and temperature the same to avoid confounding.