Case Study

Diagnose the statistical and design error in the researcher's study. Explain why her conclusion is misleading by referencing the correlation values expected across both the restricted group and the general population, and explain how she can correct her study's design.

Case context: A researcher conducts a study on the relationship between age and the enjoyment of hip hop music. Due to convenience, she only recruits participants from a local college campus who are between the ages of 1818 and 2424. After analyzing the data, she finds a Pearson's rr of 00 and publishes a paper concluding that age has no relationship to hip hop music enjoyment.

Question: Diagnose the statistical and design error in the researcher's study. Explain why her conclusion is misleading by referencing the correlation values expected across both the restricted group and the general population, and explain how she can correct her study's design.

Sample answer: The researcher committed the error of restriction of range by only sampling 1818- to 2424-year-olds. This restriction caused the correlation to drop to r=0r = 0, making the relationship appear artificially weak. Across the general population, there is actually a strong negative correlation of r=βˆ’0.77r = -0.77. To correct this design, she must sample a wide range of values (ages) to capture the overall trend accurately.

Key points:

  • Identify the issue as a restriction of range due to only sampling 1818- to 2424-year-olds.
  • Explain that range restriction obscures the relationship, dropping the correlation to r=0r = 0.
  • Contrast the restricted result with the general population's correlation of r=βˆ’0.77r = -0.77.
  • Propose correcting the design by sampling a wider range of age values.

Rubric: Grades should be based on: 1. Identifying the design error as restriction of range (3 points). 2. Contrasting the restricted sample correlation (r=0r = 0) with the general population correlation (r=βˆ’0.77r = -0.77) (4 points). 3. Explaining the correction of sampling a wider range of values/ages (3 points).

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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