Case Study

Explain how the psychologist's setup illustrates a between-subjects design. What fundamental rule of between-subjects design is applied here, and why does this setup require comparisons to be made across different groups of individuals rather than within the same individuals?

Case context: A clinical psychologist is evaluating treatments for severe agoraphobia. Following the example of a between-subjects experiment, the psychologist plans to divide a sample of 60 participants into separate groups so that each person receives only one of three possible therapies.

Question: Explain how the psychologist's setup illustrates a between-subjects design. What fundamental rule of between-subjects design is applied here, and why does this setup require comparisons to be made across different groups of individuals rather than within the same individuals?

Sample answer: This setup illustrates a between-subjects design because participants are divided into separate groups where each person receives only one of the three possible therapies. The fundamental rule applied is that each participant is exposed to only one level of the independent variable (one therapy). This setup requires comparisons across different groups because each individual only experiences one treatment, meaning the efficacy of the therapies can only be determined by comparing the outcomes of different groups of individuals against one another.

Key points:

  • Explain that participants are divided into separate groups to receive only one therapy.
  • Identify the rule that each participant is exposed to only one condition.
  • Explain that comparisons must be made between different groups of individuals since no one experiences multiple therapies.

Rubric: The student must demonstrate comprehension by explaining that dividing participants so each receives only one therapy aligns with the between-subjects requirement. They must explain that because participants do not experience multiple treatments, comparisons of the therapies' effectiveness must occur between different groups of people.

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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