Short Answer

Imagine you are applying the pretest-posttest design with switching replication to study the exercise program for depression. If you observe that both the clinical patients and the university students show a significant decrease in depression at the second measurement (before the students have started the exercise program), what does this indicate about the internal validity of your study and the actual cause of the patients' improvement?

Question: Imagine you are applying the pretest-posttest design with switching replication to study the exercise program for depression. If you observe that both the clinical patients and the university students show a significant decrease in depression at the second measurement (before the students have started the exercise program), what does this indicate about the internal validity of your study and the actual cause of the patients' improvement?

Sample answer: This indicates that the study's internal validity is compromised because a confounding variable (such as history, maturation, or testing effects) is likely responsible for the reduction in depression. Since the students improved without receiving the exercise intervention, the patients' improvement cannot be solely attributed to the exercise program itself.

Key points:

  • A decrease in depression for the waiting group (students) at the second measurement suggests an external confound.
  • Potential confounds include maturation, history, or regression to the mean.
  • The internal validity is threatened because the improvement in the treatment group (patients) cannot be confidently attributed to the exercise program.

Feedback: If both groups improve before the second group receives the treatment, the change is likely due to an external confound rather than the intervention, indicating low internal validity for attributing the cause to the exercise program.

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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