Case Study

Based on this scenario, explain why the mean reaction time of 1,445 ms is not an accurate representation of the group's performance. Support your explanation by referencing how the new mean compares to the individual scores in the dataset.

Case context: A student researcher is analyzing reaction time data from a pilot study. The initial four participants have reaction times of 200200 ms, 250250 ms, 280280 ms, and 250250 ms, which produces a mean of 245245 ms. When a fifth participant's score of 5,000 ms (suspected to be caused by participant inattention) is added, the mean increases to 1,445 ms.

Question: Based on this scenario, explain why the mean reaction time of 1,445 ms is not an accurate representation of the group's performance. Support your explanation by referencing how the new mean compares to the individual scores in the dataset.

Sample answer: The new mean of 1,445 ms is not accurate because it is heavily skewed by a single extreme outlier (5,000 ms). The calculated mean is higher than 80%80\% of the actual reaction times in the dataset (200200, 250250, 280280, and 250250 ms are all far below 1,445 ms). Therefore, the mean is pulled upwards and does not represent the behavior of any typical participant.

Key points:

  • The single outlier of 5,000 ms pulls the mean from 245245 ms to 1,445 ms.
  • The new mean (1,445 ms) is larger than 80%80\% of the scores in the dataset.
  • A measure of central tendency should represent typical behavior, but this mean is higher than almost all actual scores.

Rubric: Full credit is awarded if the student explains that the 5,000 ms outlier skews the mean, identifies that the mean of 1,445 ms is larger than 80%80\% of the scores in the dataset, and concludes that it fails to represent typical behavior.

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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