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Diagnose the methodological issue with the assistant's suggested assignment method and explain how the correct matched-groups design procedure resolves this issue to ensure equivalent groups.
Case context: Researchers planning an expressive writing study want to ensure their groups have equivalent average health before the writing manipulation begins. A research assistant suggests rank-ordering all participants by baseline health and then assigning the top 50% healthiest to the traumatic writing condition and the bottom 50% to the neutral writing condition.
Question: Diagnose the methodological issue with the assistant's suggested assignment method and explain how the correct matched-groups design procedure resolves this issue to ensure equivalent groups.
Sample answer: The assistant's method creates unequal groups: one group will be significantly healthier on average than the other. This introduces baseline health as a major confounding variable. In contrast, the correct matched-groups design pairs the two healthiest participants together and randomly assigns one to the traumatic writing condition and the other to the neutral writing condition, repeating this down the list. This paired random assignment ensures that both groups contain an equal distribution of healthy and unhealthy individuals, guaranteeing equivalent average health before the writing manipulation begins.
Key points:
- The assistant's method creates groups with unequal average health
- Baseline health would become a confounding variable rather than being controlled
- The matched-groups design pairs participants with similar health (the two healthiest, etc.)
- Random assignment within each pair distributes health levels evenly across both conditions
- The correct process guarantees equivalent average health across the two groups before the writing manipulation
Rubric: Answers must correctly diagnose that the assistant's method creates groups with unequal average health (confounding baseline health) and contrast this with the paired random assignment method which distributes health levels evenly across groups to guarantee equivalent average health.
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Research Methods in Psychology - 4th American Edition @ KPU
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