Case Study

Using your comprehension of standard deviation units and the zz score formula, explain how the psychologist should interpret the relative standings of Participant A and Participant B. Why does translating these raw scores into zz scores help the psychologist comprehend and compare their performance?

Case context: A psychologist is evaluating the cognitive test performance of two participants, Participant A and Participant B. The test scores are normally distributed with a mean of 100100 and a standard deviation of 1515. Participant A obtains a raw score of 110110, while Participant B obtains a raw score of 8585. The psychologist needs to comprehend their scores relative to the rest of the sample to decide how to describe their relative standings in a report.

Question: Using your comprehension of standard deviation units and the zz score formula, explain how the psychologist should interpret the relative standings of Participant A and Participant B. Why does translating these raw scores into zz scores help the psychologist comprehend and compare their performance?

Sample answer: The psychologist should interpret Participant A's score of 110110 as a zz score of +0.67+0.67, indicating that their performance is approximately two-thirds of a standard deviation above the mean. Participant B's score of 8585 yields a zz score of 1.00-1.00, indicating that their performance is exactly one standard deviation below the mean. Converting raw scores to zz scores helps the psychologist because it standardizes the scores, translating different raw values into a common metric (standard deviation units) that allows for direct comprehension of their relative distance from the mean.

Key points:

  • Participant A's raw score of 110110 translates to a zz score of +0.67+0.67 (approximately two-thirds of a standard deviation above the mean).
  • Participant B's raw score of 8585 translates to a zz score of 1.00-1.00 (exactly one standard deviation below the mean).
  • Translating raw scores to zz scores standardizes them into standard deviation units, allowing the psychologist to comprehend how far each participant is from the mean.

Rubric: The answer should demonstrate comprehension by: 1) Correctly interpreting Participant A's raw score of 110 as a z score of +0.67, which is approximately two-thirds of a standard deviation above the mean. 2) Correctly interpreting Participant B's raw score of 85 as a z score of -1.00, which is exactly one standard deviation below the mean. 3) Comprehending that z scores standardize raw values into standard deviation units to enable direct relative comparison.

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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