Case Study

Explain why the researcher's causal conclusion is incorrect based on the design of the study. Discuss how the directionality problem and the third-variable problem apply to this scenario.

Case context: A researcher conducts a study with a non-experimental factorial design. They measure two variables: participants' weekly caffeine consumption (High vs. Low) and their self-reported work stress (High vs. Low). They then measure participants' sleep quality. The researcher finds a correlation and publishes a paper concluding that 'high work stress and high caffeine consumption directly cause poor sleep quality.'

Question: Explain why the researcher's causal conclusion is incorrect based on the design of the study. Discuss how the directionality problem and the third-variable problem apply to this scenario.

Sample answer: The researcher's causal conclusion is incorrect because the study is a non-experimental factorial design where both independent variables (work stress and caffeine consumption) were measured rather than manipulated. Due to the directionality problem, it is possible that poor sleep causes increased caffeine consumption or higher work stress, rather than the other way around. Due to the third-variable problem, an unmeasured variable (such as an underlying health condition or general anxiety) could be causing both the elevated stress/caffeine use and the poor sleep quality.

Key points:

  • The study is non-experimental because variables are measured rather than manipulated.
  • The directionality problem applies because the direction of cause and effect between sleep quality, work stress, and caffeine consumption is ambiguous.
  • The third-variable problem applies because an unmeasured variable (like general anxiety or a medical condition) could cause the observed relationships.

Rubric: The response must explain that causality cannot be inferred because the independent variables were measured and not manipulated. It must explain the directionality problem (e.g., poor sleep causing stress/caffeine use) and the third-variable problem (e.g., a third variable like general anxiety causing both) in the context of this study.

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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