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 (the pretest) and again after the intervention (the posttest). This allows researchers to compare the results and determine if any changes occurred due to the treatment. This design is commonly used in fields like education and psychology to evaluate programs or therapies. By analyzing the differences between the pretest and posttest scores, researchers can draw conclusions about the effectiveness of the intervention and make informed decisions for future practices.