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Based on the quantitative threshold for outliers using zz scores, explain whether the researcher should formally classify this student's sleep duration as an outlier. Justify your decision by explaining what a zz score of 3.12-3.12 means conceptually in relation to the sample mean and standard deviation.

Case context: A health psychologist is investigating the sleep patterns of college students during final exams week. Out of a sample of 150 students, most report sleeping between 5 and 8 hours. However, one student reports sleeping only 1.5 hours. To decide whether to treat this extreme value as a formal outlier, the researcher calculates the zz score for this student's sleep duration and obtains a zz score of 3.12-3.12.

Question: Based on the quantitative threshold for outliers using zz scores, explain whether the researcher should formally classify this student's sleep duration as an outlier. Justify your decision by explaining what a zz score of 3.12-3.12 means conceptually in relation to the sample mean and standard deviation.

Sample answer: Yes, the researcher should formally classify the sleep duration of 1.5 hours as an outlier. Quantitatively, outliers are defined as scores with a zz score strictly less than 3.00-3.00 or strictly greater than +3.00+3.00. Because the student's zz score is 3.12-3.12, which is strictly less than 3.00-3.00, it meets this criterion. Conceptually, a zz score of 3.12-3.12 indicates that the student's sleep duration falls more than three standard deviations (specifically, 3.12 standard deviations) below the mean sleep duration of the sample.

Key points:

  • The score is formally classified as an outlier.
  • The calculated zz score of 3.12-3.12 is strictly less than the outlier threshold of 3.00-3.00.
  • A zz score of 3.12-3.12 indicates the value is more than three standard deviations below the mean.

Rubric: The response must correctly decide that the score is classified as an outlier, reference the standard threshold (strictly less than 3.00-3.00), and explain that the zz score represents falling more than three standard deviations below the mean.

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Updated 2026-05-26

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Research Methods in Psychology - 4th American Edition @ KPU

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