Case Study

Explain why evaluating a tt score of 1.501.50 requires examining both directions of the distribution when 'extreme' is defined as being far from zero, and explain what the resulting pp-value of .14.14 represents in terms of the null hypothesis distribution.

Case context: A student researcher is running a study comparing reaction times and obtains a tt score of 1.501.50 based on a sample of 2525. They determine that the proportion of tt scores that are 1.501.50 or above or that are 1.50-1.50 or below is .14.14. The researcher's advisor asks them to explain what this .14.14 means conceptually, specifically why they must consider both the positive and negative directions in their explanation.

Question: Explain why evaluating a tt score of 1.501.50 requires examining both directions of the distribution when 'extreme' is defined as being far from zero, and explain what the resulting pp-value of .14.14 represents in terms of the null hypothesis distribution.

Sample answer: When extreme is defined as being far from zero in either direction, it means any value that is at least as far from zero in either the positive or negative direction is considered extreme. Therefore, we must include the proportion of tt scores that are 1.501.50 or above and those that are 1.50-1.50 or below. The resulting pp-value of .14.14 represents the total proportion of these extreme tt scores in the distribution, indicating a 14% chance of obtaining a tt score at least this extreme by chance.

Key points:

  • Extreme values far from zero must be accounted for in both directions.
  • The evaluation must sum the proportions of tt scores that are 1.501.50 or above and 1.50-1.50 or below.
  • The pp-value represents the combined proportion of these extreme scores in the distribution.

Rubric: The student must show comprehension of a two-tailed test by explaining that 'far from zero in either direction' requires including both positive and negative extremes. They must also explain that the pp-value of .14.14 represents the combined proportion of these extreme regions in the distribution.

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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