Case Study

Analyze Dr. Vance's conclusion using the 'limited informativeness of rejecting the null hypothesis' critique. Diagnose the issue with her justification and explain why her large sample size makes this finding particularly susceptible to this criticism.

Case context: Dr. Vance is evaluating a new study skills workshop with a sample of 10,000 college students. She runs a hypothesis test comparing the workshop group to a control group and finds a statistically significant difference in final exam scores (p=.04p = .04). Based on this significance, Dr. Vance declares the workshop a major success and recommends that all universities implement it immediately.

Question: Analyze Dr. Vance's conclusion using the 'limited informativeness of rejecting the null hypothesis' critique. Diagnose the issue with her justification and explain why her large sample size makes this finding particularly susceptible to this criticism.

Sample answer: Dr. Vance is assuming that a statistically significant result (p<.05p < .05) automatically translates to a meaningful real-world effect. However, rejecting the null hypothesis only indicates that the difference in exam scores is not exactly zero; it does not specify the magnitude of the difference. With a very large sample size (N=10,000N = 10,000), even a tiny, practically trivial difference in exam scores can become statistically significant. Therefore, her recommendation is unjustified because the actual effect size could be negligible, and simply confirming a nonzero difference is uninformative without reporting the magnitude of the effect.

Key points:

  • Conflates statistical significance with practical real-world significance.
  • Null hypothesis rejection only asserts a nonzero relationship, not its magnitude.
  • Large sample sizes can easily detect tiny, trivial relationships as statistically significant.
  • Fails to provide or analyze effect size to justify recommending the workshop.

Rubric: The response should: 1. Diagnose the conflation of statistical significance with practical significance. 2. Explain that rejecting the null hypothesis only tells us the difference is nonzero. 3. Analyze how the large sample size makes the test highly sensitive to tiny, practically insignificant differences. 4. Explain why effect size must be reported to justify her recommendation.

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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