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Based on the case context, analyze how Dr. Rivera should interpret the results of her pretest-posttest nonequivalent groups design to determine if the wellness program was effective. What specific comparison must she make, and why does the decrease in both groups not necessarily invalidate the program's effectiveness?
Case context: Dr. Rivera is evaluating a new workplace wellness program at a large corporation. She selects the marketing department to participate in the program and the accounting department to serve as the nonequivalent control group. She measures employee stress levels in both departments in January (before the program) and again in June (after the marketing department completes the program). Dr. Rivera notices that stress levels decreased in both departments from January to June.
Question: Based on the case context, analyze how Dr. Rivera should interpret the results of her pretest-posttest nonequivalent groups design to determine if the wellness program was effective. What specific comparison must she make, and why does the decrease in both groups not necessarily invalidate the program's effectiveness?
Sample answer: Dr. Rivera must compare the pretest-to-posttest change in the marketing department against the pretest-to-posttest change in the accounting department. The decrease in stress for both groups does not invalidate the program because general maturation or historical events (like a less busy season in June) might have caused stress to drop company-wide. To prove the program's effectiveness, she must determine if the marketing department demonstrated a significantly greater improvement (a larger decrease in stress) than the accounting department.
Key points:
- The critical comparison is the pretest-to-posttest change between the treatment and control groups.
- Both groups decreasing might simply be due to general maturation or historical effects.
- The program is considered effective only if the treatment group shows significantly greater improvement than the control group.
- Comparing the change scores isolates the treatment effect from natural environmental shifts.
Rubric: The student should identify that the analysis relies on comparing the magnitude of change between the two groups rather than simply looking at the final posttest scores, and analyze how evaluating change accounts for external variables like historical effects.
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Research Methods in Psychology - 4th American Edition @ KPU
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