Case Study

Based on your understanding of zz scores, explain what these calculations indicate about the positions of Participant A and Participant B relative to the mean of the distribution. How do the sign and value of each student's zz score convey their relative cognitive performance score compared to the average population?

Case context: A psychology researcher measures the IQ scores of two participants. The distribution of intelligence quotient (IQ) scores in the general population has a mean of 100100 and a standard deviation of 1515. Participant A has an IQ of 110110 (z=+0.67z = +0.67), and Participant B has an IQ of 8585 (z=1.00z = -1.00).

Question: Based on your understanding of zz scores, explain what these calculations indicate about the positions of Participant A and Participant B relative to the mean of the distribution. How do the sign and value of each student's zz score convey their relative cognitive performance score compared to the average population?

Sample answer: Participant A's zz score of +0.67+0.67 indicates their score is approximately two-thirds of a standard deviation above the mean. The positive sign shows they performed above average. Participant B's zz score of 1.00-1.00 indicates their score is exactly one standard deviation below the mean, with the negative sign showing they performed below average. This allows the researcher to comprehend that Participant A scored higher than average while Participant B scored lower than average by one standard deviation unit.

Key points:

  • Explain that a positive zz score indicates a value above the mean
  • Explain that a negative zz score indicates a value below the mean
  • Interpret +0.67+0.67 as approximately two-thirds of a standard deviation above the mean
  • Interpret 1.00-1.00 as exactly one standard deviation below the mean

Rubric: The answer should demonstrate a clear comprehension of how zz scores represent distance and direction from the mean, specifically interpreting +0.67+0.67 as two-thirds of a standard deviation above the mean and 1.00-1.00 as exactly one standard deviation below the mean.

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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