A pretest-posttest design is a research method used to measure the effects of an intervention or treatment. In this design, participants are assessed before the intervention (pretest) and then again after the intervention (posttest). This allows researchers to compare the results and determine if any changes occurred as a result of the treatment. This design is commonly used in fields like education, psychology, and healthcare to evaluate programs or therapies. By analyzing the differences between pretest and posttest scores, researchers can draw conclusions about the effectiveness of the intervention and make informed decisions for future practices.