Definition

Independent and dependent variables

The independent variable is what you manipulate or compare; the dependent variable is the outcome you measure to see the effect.

In an experiment, the independent variable (IV) is under your control — treatment vs placebo, interface A vs B — and the dependent variable (DV) is what you record: symptoms, task time, test scores. Hypotheses are statements about how the IV moves the DV.

In observational studies the same roles appear as predictor/exposure and outcome, without manipulation — which is exactly why causal claims get harder. Confounders are variables that influence both, and controlling for them is the central design problem.