The dynamic nature of injunctive drinking norms and within-person associations with college student alcohol use.

Objective: Perceptions of friends' approval of drinking behaviors (i.e., injunctive drinking norms) play a central role in shaping college students' alcohol use behaviors. However, we know little about the extent that students' perceptions of friends' approval fluctuate over time and whether there are within-person associations between these injunctive norms and alcohol use. To fill this knowledge gap, we estimated within-person variability in perceptions of friends' approval of alcohol use across a 12-month period and examined within-person associations between perceptions of friends' approval and 3 discrete drinking behaviors: number of weekly drinks, hazardous drinking behaviors, and peak estimated blood-alcohol content (peak-eBAC). Method: A sample of college students (N = 433, 54.82% female, Mage = 20.06) reported perceptions of friends' approval of alcohol use and indices of alcohol use behavior at 4 timepoints across a single year. Results: Descriptive estimates of within-person variability of perceived friends' approval revealed that these perceptions fluctuated considerably across the 4 timepoints. After accounting for between-person effects, longitudinal multilevel modeling revealed significant within-person associations between perceptions of friends' approval and (a) number of weekly drinks, (b) hazardous drinking behaviors, and (c) peak-eBAC levels. Students reported heavier alcohol use at timepoints when they perceived their friends as being more approving than usual. Conclusions: Alongside advancing theoretical understanding of social influences on students' alcohol use, the current findings hold important clinical implications for norms-based harm-reduction strategies. To optimize interventions, norms-based approaches may need to be adaptive over time (e.g., boosters) to map onto within-person fluctuations in perceived injunctive norms. (PsycInfo Database Record (c) 2021 APA, all rights reserved).