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Case Study

Based on the definition of a linear relationship, classify the associations found in Study A and Study B. Explain your reasoning for each classification using the characteristics of linear relationships.

Case context: A research methodology student is reviewing scatterplots from two different psychology studies. Study A plots the relationship between 'hours of sleep' and 'number of memory errors', showing points that cluster closely around a straight line sloping downwards. Study B plots 'stress level' and 'task performance', showing points that rise in a straight line initially, but then curve downwards in a U-shape at higher stress levels.

Question: Based on the definition of a linear relationship, classify the associations found in Study A and Study B. Explain your reasoning for each classification using the characteristics of linear relationships.

Sample answer: Study A demonstrates a linear relationship because the data points are reasonably well fit by a single straight line (specifically, a negative correlation). Study B does not demonstrate a linear relationship because the points form a curve (a U-shape) rather than a straight linear trend.

Key points:

  • Diagnoses Study A as having a linear relationship.
  • Justifies Study A by noting the straight linear trend of the downward slope.
  • Diagnoses Study B as not having a linear relationship.
  • Justifies Study B by noting that the points form a curve rather than a straight line.

Rubric: The student must correctly identify Study A as a linear relationship (or negative correlation) and Study B as non-linear. The explanation must reference that linear relationships require points to be well fit by a single straight line, not a curve.

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Updated 2026-05-27

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KPU

Research Methods in Psychology - 4th American Edition @ KPU

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