Explain the purpose of the treatment removal phase for the patient group in this design. How does the expected change in their depression levels after treatment removal help researchers demonstrate that the exercise intervention is the actual cause of the changes in depression?
Case context: A research group conducts an exercise intervention study with two nonequivalent groups (depressed patients and depressed students) using a switching replication with treatment removal design. After establishing baselines, patients receive the exercise program while students do not. Later, the researchers instruct the patients to stop exercising and instruct the students to start exercising. The researchers want to understand why they must remove the treatment from the first group rather than just letting them continue exercising.
Question: Explain the purpose of the treatment removal phase for the patient group in this design. How does the expected change in their depression levels after treatment removal help researchers demonstrate that the exercise intervention is the actual cause of the changes in depression?
Sample answer: The purpose of the treatment removal phase is to show that the initial improvement was directly caused by the intervention. If the exercise program is the cause of decreased depression, then removing the program should cause patients' depression levels to increase again. If their depression levels had remained low even after stopping exercise, it would be harder to rule out external factors (such as spontaneous recovery or historical events) as the cause of the initial decrease.
Key points:
- Treatment removal tests if the improvement is maintained without the intervention
- Depression levels in the patient group are expected to increase after exercise is stopped
- This reversal supports the causal link between the exercise intervention and depression reduction
- It helps rule out threats to internal validity like history or spontaneous improvement
Rubric: Ensure the student mentions: 1. The treatment removal is designed to show the dependency of the improvement on the presence of the treatment. 2. The expected outcome is that patients' depression levels increase after stopping exercise. 3. This pattern helps rule out alternative explanations like history or maturation, establishing a stronger causal link.
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Research Methods in Psychology - 4th American Edition @ KPU
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