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Explain why comparing the pretest-to-posttest changes between the treatment group and the control group allows the researcher to comprehend and isolate the actual effect of the memory-training program from alternative explanations.
Case context: A researcher is studying the effectiveness of a new memory-training program for older adults. They recruit 80 participants, assigning 40 to the memory-training program (treatment group) and 40 to a waitlist (control group). Both groups take a memory assessment at the beginning (pretest) and at the end of 8 weeks (posttest). Over the course of the 8 weeks, all participants experience normal cognitive changes, get used to the memory assessment environment, and live through identical daily external events.
Question: Explain why comparing the pretest-to-posttest changes between the treatment group and the control group allows the researcher to comprehend and isolate the actual effect of the memory-training program from alternative explanations.
Sample answer: Comparing the two groups allows the researcher to isolate the actual effect of the program because both groups are subject to the same internal validity threats, such as maturation (normal cognitive changes), testing (getting used to the assessment), and history (external events). Since these factors affect both groups equally, comparing the differences in their posttest changes allows the researcher to subtract these alternative explanations and isolate the treatment's true effect.
Key points:
- Explains that threats like maturation, testing, and history affect both groups in the same way.
- Explains that comparing changes between the groups subtracts these shared effects.
- Concludes that this comparison isolates the actual effect of the treatment.
Rubric: The response must explain: 1) That threats like maturation, testing, and history affect both groups similarly because they share the timeline and testing conditions. 2) That comparing the posttest changes between the treatment and control groups allows the researcher to subtract the common changes, isolating the unique effect of the treatment.
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Research Methods in Psychology - 4th American Edition @ KPU
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