Case Study

Explain what each of the three separate statistical outputs (the main effect of major, the main effect of food type, and the interaction effect) measures in the context of this calorie estimation study. How does the researcher use these outputs to understand the factors influencing calorie estimation?

Case context: A health psychologist is conducting a study on calorie estimation. They use a factorial design with two independent variables: participant major (psychology versus nutrition) and food type (cookie versus hamburger). To analyze the data, the psychologist runs a factorial ANOVA, which yields separate FF ratios and pp-values for the main effect of participant major, the main effect of food type, and the interaction effect between the two variables.

Question: Explain what each of the three separate statistical outputs (the main effect of major, the main effect of food type, and the interaction effect) measures in the context of this calorie estimation study. How does the researcher use these outputs to understand the factors influencing calorie estimation?

Sample answer: In this study, the three outputs measure different aspects of calorie estimation: 1. The main effect of the participant's major evaluates whether there is an overall difference in calorie estimates between psychology majors and nutrition majors, ignoring the type of food. 2. The main effect of the food type evaluates whether there is an overall difference in calorie estimates between cookies and hamburgers, ignoring the participant's major. 3. The interaction effect evaluates whether the difference in calorie estimates between psychology and nutrition majors varies depending on whether they are estimating a cookie or a hamburger. The researcher uses these outputs to determine which factors independently influence estimation and whether their combined influence is interdependent.

Key points:

  • The main effect of major compares calorie estimates between psychology and nutrition majors overall.
  • The main effect of food type compares calorie estimates between cookies and hamburgers overall.
  • The interaction effect assesses if the effect of major on calorie estimates depends on the food type.

Rubric: To receive full marks, the response must correctly explain the meaning of: (1) the main effect of participant major in comparing the two majors, (2) the main effect of food type in comparing the two food categories, and (3) the interaction effect in showing how the effect of one variable depends on the other.

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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