Peer influence on grocery purchases: Experimental design practice

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Here’s some experimental design practice for your Intro Psych students. This would work right after covering experiments in the research methods chapter or as an experimental design booster in the social psych chapter.

Ask students to read this Science Daily summary of an experiment on grocery purchases (Shin et al., 2024), and then work in small groups to answer the following questions.

1. The article does not explicitly say what the research hypothesis was. However, based on the information given, what do you believe their primary research hypothesis was?
2. What was the independent variable? Identify each level of the independent variable. (The experiment used a within-participants design, meaning each participant experienced each level of the independent variable.)
3. What was the primary dependent variable?
4. Briefly summarize the results.
5. This study was conducted in a virtual grocery store using virtual money. Can we assume researchers would see similar results in a real grocery store where consumers were using their own money? Why or why not?
6. Using the same independent variable and dependent variable, describe how this study could be conducted in the field under real-life conditions.

The original research article (Shin et al., 2024) includes photos of the online store, how the nutritional score was displayed for each item, and how the individual’s nutritional score was displayed.

If time allows, share with your students that the participants were recruited from Facebook and Instagram, were all in Singapore, were 21 years of age and older, and were the primary shopper in their household. How might each of these factors influence the results?

One last note about the within-participants design. The researchers noted this design as a study limitation in their research article (Shin et al., 2024). They acknowledged that there seemed to be carryover when participants saw nutritional labeling first followed by the control condition. Since the conditions were counterbalanced, the researchers also compared participants just based on the first store they saw. They still saw the effect of peer influence.  

Reference

Shin, S., Gandhi, M., Puri, J., & Finkelstein, E. (2024). Influencing the nutritional quality of grocery purchases: A randomized trial to evaluate the impact of a social norm-based behavioral intervention with and without a loss-framed financial incentive. Food Policy, 125, 102646. https://doi.org/10.1016/j.foodpol.2024.102646