Essay

Based on the textbook example of reaction times (200200, 250250, 280280, and 250250 ms), recall and state the initial mean of the dataset, the value of the added outlier, and the new mean. Explain the behavioral cause of the outlier as described in the text, and describe how this change illustrates the limitation of using the mean to represent typical behavior in a skewed distribution.

Question: Based on the textbook example of reaction times (200200, 250250, 280280, and 250250 ms), recall and state the initial mean of the dataset, the value of the added outlier, and the new mean. Explain the behavioral cause of the outlier as described in the text, and describe how this change illustrates the limitation of using the mean to represent typical behavior in a skewed distribution.

Sample answer: The initial mean of the dataset is 245245 ms. The added outlier score is 5,000 ms, which increases the mean to 1,445 ms. The text explains that this outlier was likely caused by participant inattention. This illustrates that a single extreme outlier can pull the mean so far that it is larger than 80%80\% of the scores, meaning it no longer accurately represents typical behavior in the distribution.

Key points:

  • The initial mean of the reaction times is 245245 ms.
  • The added outlier value is 5,000 ms.
  • The new mean after the outlier is added is 1,445 ms.
  • The outlier occurred due to participant inattention.
  • The new mean is higher than 80%80\% of the scores in the distribution.

Rubric: Full credit is awarded if the student recalls the original mean of 245245 ms, the outlier value of 5,000 ms, the new mean of 1,445 ms, identifies the cause of the outlier as participant inattention, and explains that the new mean exceeds 80%80\% of the scores, failing 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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