What is the difference between an independent variable and a dependent variable?

The independent variable is the factor the researcher deliberately manipulates or changes to observe its effect. The dependent variable is the outcome that is measured to see if it was affected by the manipulation. A simple way to remember is that the dependent variable depends on what the researcher does with the independent variable. For example, in a study testing whether caffeine improves reaction time, caffeine dose is the independent variable and reaction time is the dependent variable. The experimental group receives the treatment while the control group does not, allowing comparison.