Control Group in Pretest-Posttest Designs

Example of Regression to the Mean

In a research study, what condition primarily makes regression to the mean a severe threat to internal validity?

If a researcher specifically selects participants for an intervention because they scored in the extreme bottom 5% on a pretest, any subsequent improvement on their posttest scores can be confidently attributed solely to the effectiveness of the intervention.

A researcher is studying the impact of a new intensive reading program. Arrange the following steps in the correct order to illustrate how 'regression to the mean' acts as a severe threat to the internal validity of this study.

An educational researcher identifies the 30 students with the highest math-anxiety scores in a school and has them practice mindfulness for one week. On the posttest, their average anxiety scores have dropped significantly. Match each component of this research scenario to the specific role it plays in creating a threat to internal validity.

As a lead researcher, you are tasked with designing a new study to test an intervention for individuals experiencing extreme bouts of insomnia. To ensure the final results are not confounded by regression to the mean, arrange the following procedural steps in the order required to construct a valid experimental design.

According to the principle of regression to the mean, if participants are selected for a study specifically because they achieved exceptionally high pretest scores, what is the most likely statistical outcome for their posttest scores?

A researcher concludes that a new study-skills workshop is successful because the students who scored in the bottom $5\%$ on the first quiz showed a significant improvement on the second quiz. To evaluate the internal validity of this conclusion, one must account for the fact that these extreme scores were statistically likely to move closer to the group average due to _____ to the mean.

A researcher measures depressive symptoms in college students and recruits only the top $10\%$ most depressed students to participate in a new mindfulness intervention. At the end of the semester, the students' depressive symptoms decrease. In this design, regression to the mean is a major threat to internal validity because these participants were selected based on their extreme initial scores.

Match the pretest score scenario with its corresponding posttest tendency or statistical explanation under the threat of regression to the mean.

A clinical psychologist evaluates a new therapy for anxiety. She selects the $15$ patients with the highest anxiety scores from a clinic. After ten sessions of therapy, their anxiety scores decrease significantly. To evaluate the internal validity of this study, we must recognize that because participants were chosen for their extreme scores, the improvement is confounded by statistical _____.