Case Study

Using the concepts of central tendency and variability, explain how the researcher should interpret and compare the spread of reaction times in Group A and Group B, and explain why relying solely on central tendency would lead to an incomplete understanding of the two groups' performances.

Case context: A psychology researcher measures the reaction times (in seconds) of two different groups of participants on a cognitive task. Both Group A and Group B have a mean, median, and mode reaction time of exactly 1010 seconds. However, when plotting the data, the researcher observes that Group A's scores are all clustered tightly between 99 and 1111 seconds, whereas Group B's scores are spread widely between 22 and 1818 seconds.

Question: Using the concepts of central tendency and variability, explain how the researcher should interpret and compare the spread of reaction times in Group A and Group B, and explain why relying solely on central tendency would lead to an incomplete understanding of the two groups' performances.

Sample answer: The researcher should interpret Group A as having relatively low variability because its scores are clustered close to the center (1010 seconds). Group B has relatively high variability because its scores are spread across a much greater range (22 to 1818 seconds). Relying solely on the central tendency would lead to an incomplete understanding because both groups appear identical (mean, median, and mode of 1010 seconds), masking the significant difference in how consistent or spread out the individual performance scores are.

Key points:

  • Group A exhibits low variability with scores clustered close to the central tendency of 1010 seconds.
  • Group B exhibits high variability with scores spread across a much wider range (22 to 1818 seconds).
  • Central tendency alone fails to capture the differences in the spread or dispersion of the scores between the two groups.

Rubric: The answer must accurately: 1. Identify Group A as having low variability and explain it in terms of scores clustering close to the center. 2. Identify Group B as having high variability and explain it in terms of scores spreading across a wider range. 3. Explain that central tendency alone masks differences in the spread/variability of scores.

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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