Case Study

Explain why this design is represented as a 2×2×22 \times 2 \times 2 factorial design and explain how the interaction between these multiple independent variables could provide deeper insights into psychotherapy outcomes than studying each variable individually.

Case context: A research group is studying psychological treatments and wants to design an experiment based on the example. They select three factors: type of psychotherapy (cognitive vs. behavioral), treatment duration (two weeks vs. two months), and the sex of the psychotherapist (female vs. male). They are presenting their research proposal to a review board, and they must justify their choice of a 2×2×22 \times 2 \times 2 factorial design over running three separate single-factor experiments.

Question: Explain why this design is represented as a 2×2×22 \times 2 \times 2 factorial design and explain how the interaction between these multiple independent variables could provide deeper insights into psychotherapy outcomes than studying each variable individually.

Sample answer: The design is represented as 2×2×22 \times 2 \times 2 because it involves three independent variables, each containing exactly two levels. When multiplied, they form eight unique conditions. Choosing this factorial design allows researchers to examine not just the main effects of each variable, but also the interaction effects. For example, it helps determine if the effectiveness of a specific therapy type depends on its duration, or if it interacts with the sex of the therapist. This complexity cannot be captured by running three separate single-factor experiments.

Key points:

  • Explain that the three numbers in the notation represent three distinct independent variables.
  • Explain that each number '2' represents the number of levels for that specific independent variable.
  • Discuss how factorial designs allow for the analysis of interaction effects between the independent variables.
  • Contrast the ability to detect interactions in a factorial design with the limitations of separate single-factor experiments.

Rubric: The response must explain what the notation '2×2×22 \times 2 \times 2' means (three variables, two levels each) and explain that factorial designs allow for the detection of interaction effects between variables, which separate single-factor experiments cannot do.

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Updated 2026-05-26

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Research Methods in Psychology - 4th American Edition @ KPU

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