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Case Study

Analyze the difference between Study A and Study B. Identify which determinant of the pp value explains the difference in their statistical significance, and explain the statistical mechanism behind why this determinant led to a lower pp value for Study B.

Case context: Dr. Aris is reviewing the results of two independent experiments testing the effect of a mindfulness app on stress. Study A found a moderate difference in stress levels between the app group and control group with a sample size of N=30N = 30, resulting in a pp value of .08.08. Study B observed the exact same moderate difference in stress levels but utilized a sample size of N=150N = 150, resulting in a pp value of .02.02.

Question: Analyze the difference between Study A and Study B. Identify which determinant of the pp value explains the difference in their statistical significance, and explain the statistical mechanism behind why this determinant led to a lower pp value for Study B.

Sample answer: The determinant explaining the difference in statistical significance is the sample size. Both studies observed the exact same strength of relationship (moderate difference in stress levels). However, Study B used a much larger sample size (N=150N = 150) compared to Study A (N=30N = 30). Under null hypothesis testing, a larger sample size decreases the probability of obtaining the observed result if the null hypothesis were true. Because of this, the larger sample size in Study B resulted in a lower pp value (.02.02) compared to Study A (.08.08).

Key points:

  • Identify that the strength of the relationship is identical in both studies.
  • Identify sample size as the determinant that differs between Study A and Study B.
  • Analyze that the larger sample size of Study B (N=150N = 150) is responsible for its lower pp value (.02.02).
  • Explain the mechanism: a larger sample size decreases the probability of obtaining the observed result if the null hypothesis were true.

Rubric: The response must correctly identify sample size as the differing determinant since relationship strength is held constant. It must explain that a larger sample size decreases the probability of obtaining the observed result if the null hypothesis were true, leading to a lower pp value.

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Updated 2026-05-26

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Research Methods in Psychology - 4th American Edition @ KPU

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