Experimental Methods

The experiment is psychology's most powerful tool for establishing cause and effect. Its central logic is simple but demanding: a researcher deliberately changes one thing and measures whether another thing changes as a result. The variable the researcher manipulates is the independent variable (IV), and the variable that is measured to detect an effect is the dependent variable (DV). For example, a psychologist studying memory might manipulate the amount of sleep participants have (the IV) and measure their score on a recall test (the DV). Because the researcher controls the IV rather than merely observing it, a well-designed experiment can support a causal claim in a way that no other method can.

Every experiment begins with a hypothesis, a precise, testable prediction about the relation