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Case Study

Based on the provided context, identify the outlier, explain how its inclusion alters the calculated range compared to the range of the other nine participants, and explain why the resulting range is a misleading representation of the group's general performance variability.

Case context: A psychology researcher administers a memory test to a group of 10 participants. Nine of the participants score between 90 and 100, showing very similar performance. However, one participant experiences a distraction and scores a 20. The researcher calculates the range of the scores to describe the overall variability of the group's memory performance.

Question: Based on the provided context, identify the outlier, explain how its inclusion alters the calculated range compared to the range of the other nine participants, and explain why the resulting range is a misleading representation of the group's general performance variability.

Sample answer: The outlier in this dataset is the score of 20. Without this score, the range for the remaining nine participants is 10 (100 - 90). Including the outlier changes the range to 80 (100 - 20). This resulting range of 80 is misleading because it suggests the group's memory scores are highly variable, whereas in reality, 90% of the participants scored within a very narrow, high-performing window of 10 points.

Key points:

  • Identify the score of 20 as the outlier.
  • Explain that the range increases from 10 to 80 with the outlier's inclusion.
  • Demonstrate comprehension that the range of 80 misrepresents the low variability of the majority of the scores.

Rubric: The response must identify the score of 20 as the outlier, calculate or contrast the two ranges (10 vs 80), and explain that the range of 80 falsely implies high overall variability when most participants performed very similarly.

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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