In an experiment, what is the independent variable?

• A. The variable that is deliberately changed by the experimenter
• B. The variable kept constant
• C. The variable that depends on the result
• D. The variable measured

Answer: (A)

The main idea here is what you control to see if it causes a difference. The independent variable is the factor you deliberately change to test its effect on something else. For example, if you want to know how the amount of sunlight affects how tall a plant grows, the amount of sunlight is the independent variable because you set it at different levels to observe what happens. The thing you measure to see the result—usually the plant’s height—is the dependent variable. Variables you keep the same to make the test fair, like soil type or water amount, are constants (often called controlled variables). So the option describing the variable you actively change is the best fit, while the others describe the result you measure or the things you keep constant.