Case Study

Diagnose why the student's planned conclusion is misleading based on the concepts of main effects and interactions. Comprehending how interactions qualify main effects as shown in the Schnall et al. study, describe what statistical analysis the student should perform to resolve this and what the analysis would reveal.

Case context: A student researcher is investigating how an environmental stressor (noise level: loud vs. quiet) affects academic test performance. They also measure a potential moderator: trait anxiety (high vs. low). Preliminary analyses show a significant main effect where loud noise leads to lower academic performance. However, they also find a significant interaction between noise level and trait anxiety. The student wants to write in their research report that loud noise universally impairs academic performance.

Question: Diagnose why the student's planned conclusion is misleading based on the concepts of main effects and interactions. Comprehending how interactions qualify main effects as shown in the Schnall et al. study, describe what statistical analysis the student should perform to resolve this and what the analysis would reveal.

Sample answer: The student's conclusion is misleading because the significant interaction shows that the effect of noise level on performance depends on trait anxiety; therefore, the main effect is not universal. To resolve this, the student must conduct simple effects analyses. This statistical step will test the effect of noise level (loud vs. quiet) separately at each level of trait anxiety (high and low). This will reveal whether the impairment from loud noise occurs for both anxiety groups or only under specific conditions (for example, only for high-anxiety individuals), clarifying the interaction.

Key points:

  • Explain that reporting the main effect as a universal finding is misleading because the interaction indicates the effect of noise depends on trait anxiety.
  • Identify simple effects analyses as the statistical method needed to unpack the interaction.
  • Explain that simple effects analyses test the effect of the noise level separately for high-anxiety and low-anxiety participants.

Rubric: The response must explain that a main effect is misleading when a significant interaction is present because the effect depends on the moderator, identify simple effects analyses as the correct follow-up method, and explain that it tests the independent variable's effect at each level of the moderator.

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Updated 2026-05-26

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Research Methods in Psychology - 4th American Edition @ KPU

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