The power of regression to the mean: a social norm study revisited

This research follows up on a study by Schultz et al. (2007), in which the effect of a social norm intervention on energy consumption was examined. The present studies included control groups to examine whether social norm effects would persist beyond regression to the mean. Both studies had a 2 (baseline consumption: below mean versus above mean) × 2 (message condition: no-message control versus norm message) design. Based on baseline fruit (Study 1) or unhealthy snack (Study 2) consumption, students were classified as above mean or below mean for consumption. One week later, half of the students in the above-mean and below-mean groups received normative feedback; control groups did not. Neither study showed an effect of norm messages on behavior relative to control, providing evidence for regression to the mean as an alternative explanation. Findings highlight the importance of control groups to distinguish social norm intervention effects from mere regression to the mean.