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

Random assignment is used in experimental research to ensure that any differences between the experimental group and the control group are due to the treatment being studied and not other factors. By randomly assigning participants to either the experimental or control group, the researcher is able to minimize preexisting differences between the groups and increase the internal validity of the study.

Option A is incorrect because random assignment does not guarantee treatment effectiveness, it only helps determine if the treatment is the reason for any differences between groups.

Option B is incorrect because random assignment does not directly measure the dependent variable, it helps control for other variables that may impact the dependent variable.

Option D is incorrect because random assignment is necessary for a control condition in experimental research. Without a control condition, it is impossible to determine if the treatment had an effect or if other factors were responsible.