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Case Study

Diagnose the statistical flaw in the research team's data analysis plan, and explain what their shared goal should be when selecting an alternative analysis procedure.

Case context: A research team conducts an experiment with five different treatment groups and finds a significant overall effect. They decide to compare every possible pair of groups using standard tt-tests to see which specific treatments differ from each other.

Question: Diagnose the statistical flaw in the research team's data analysis plan, and explain what their shared goal should be when selecting an alternative analysis procedure.

Sample answer: The flaw is that using standard tt-tests for multiple post hoc comparisons inflates the overall risk of making a Type I error. Their shared goal should be to select a modified procedure that keeps the overall risk of mistakenly rejecting a true null hypothesis at an acceptable level, typically close to 5%5\%.

Key points:

  • Standard t-tests inflate Type I error risk
  • Alternative procedures keep the error risk at an acceptable level
  • The overall acceptable level is typically close to 5%

Rubric: Award full credit if the student accurately diagnoses the inflation of Type I error risk and explains that the goal of alternative procedures is to maintain an acceptable overall error rate.

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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