AP Psychology Practice Test 2026 - Free AP Psychology Practice Questions and Study Guide

The purpose of an experiment in research is fundamentally to manipulate one or more independent variables to observe their effect on one or more dependent variables. This manipulation allows researchers to establish cause-and-effect relationships, which is essential for understanding how different factors interact. By controlling the conditions under which the variables are tested, researchers can isolate specific influences and draw conclusions about causal relationships.

In contrast, surveying a random sample of the population is typically associated with correlational research, where the aim is to gather data without manipulation to understand patterns or trends rather than causation. Detailed observations of a single subject refers to a case study approach, which provides in-depth insights but may not allow for generalization or the testing of broad hypotheses. Measuring the correlation between two variables, on the other hand, examines the degree to which two variables are related but does not involve manipulation and, therefore, lacks the capability to infer direct causality.