Case Study

Based on the characteristics of central tendency in a bimodal distribution, explain why reporting the mean or median as a single typical score might be unrepresentative of either group, and identify which measure of central tendency would correspond to the tallest peak.

Case context: A cognitive psychologist collects reaction time data on a task and plots the frequency distribution. The resulting graph is bimodal, showing one peak representing fast automatic responses and a taller peak representing slower controlled responses. The researcher wants to summarize the typical score using central tendency.

Question: Based on the characteristics of central tendency in a bimodal distribution, explain why reporting the mean or median as a single typical score might be unrepresentative of either group, and identify which measure of central tendency would correspond to the tallest peak.

Sample answer: Reporting the mean or median as the typical score would be unrepresentative because both measures will typically fall in the middle between the two peaks, where very few data points actually lie. Instead, the researcher should look to the mode, as it is located exclusively at the tallest peak of the distribution.

Key points:

  • The mean and median fall in the middle between the two peaks in a bimodal distribution.
  • A central value between peaks may fail to represent either group's typical score.
  • The mode corresponds exclusively to the tallest peak.

Rubric: Grading Rubric: - 5 pts: Explains that the mean and median fall between the peaks, making them poor representations of the actual clusters of scores. - 5 pts: Correctly identifies that the mode corresponds to the tallest peak of the distribution.

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Updated 2026-05-26

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Research Methods in Psychology - 4th American Edition @ KPU

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