Case Study

Based on this scenario, diagnose the relationship between central tendency and variability for the two groups. Contrast the distributions of Group A and Group B using the concepts of low and high variability.

Case context: A cognitive psychologist measures reaction times on a computer task for two different groups of participants. Both Group A and Group B have a mean reaction time of 400 milliseconds, a median of 400 milliseconds, and a mode of 400 milliseconds. However, the scores in Group A are tightly clustered between 390 ms and 410 ms, whereas the scores in Group B range widely from 200 ms to 600 ms.

Question: Based on this scenario, diagnose the relationship between central tendency and variability for the two groups. Contrast the distributions of Group A and Group B using the concepts of low and high variability.

Sample answer: Both Group A and Group B share the identical central tendency because their mean, median, and mode are all 400 ms. However, they differ in variability. Group A has low variability because its scores are clustered closely around the center (390 ms to 410 ms). Group B has high variability because its scores are spread across a much broader range (200 ms to 600 ms). This illustrates that distributions can share the exact same central tendency yet have completely different variability.

Key points:

  • Identifies that both groups share the identical central tendency (mean, median, and mode are all 400 ms).
  • Explains that Group A exhibits low variability because its scores are clustered closely around the center.
  • Explains that Group B exhibits high variability because its scores are spread across a much broader range.
  • Recognizes that central tendency and variability are distinct properties of a distribution.

Rubric: The response should correctly identify that central tendencies are identical for both groups. It should identify Group A as having low variability and explain what that means in this context (scores close to 400 ms). It should identify Group B as having high variability and explain what that means in this context (scores spread widely from 200 ms to 600 ms).

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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