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Case Study

Based on your understanding of within-subjects experimental designs, diagnose the specific problem that could explain the researcher's observation instead of the lighting itself. Explain how this problem operates in this specific scenario.

Case context: A researcher is studying the effect of lighting on reading speed using a within-subjects design. Every participant first reads a passage under dim light, followed immediately by reading a second passage under bright light. The researcher observes that all participants read the second passage significantly faster and concludes that bright light improves reading speed.

Question: Based on your understanding of within-subjects experimental designs, diagnose the specific problem that could explain the researcher's observation instead of the lighting itself. Explain how this problem operates in this specific scenario.

Sample answer: The potential problem is an order effect acting as a confounding variable. Because every participant experienced the conditions in the exact same sequence, their faster reading speed in the second condition (bright light) could be systematically affected by the order of exposure—such as gaining practice from reading the first passage—rather than being a true effect of the independent variable.

Key points:

  • Diagnoses the issue as an order effect.
  • Explains that participants' responses are systematically affected by the sequence of the conditions.
  • Identifies that the order acts as a confounding variable.
  • Recognizes that the true effect of the independent variable (lighting) is obscured.

Rubric: Full credit is awarded for correctly diagnosing an order effect and explaining that the responses in the bright light condition may be systematically affected by being exposed to the sequence of conditions rather than the independent variable.

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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