The social norms of birth cohorts and adolescent marijuana use in the United States, 1976-2007.

AIMS Studies of the relationship between social norms and marijuana use have generally focused on individual attitudes, leaving the influence of larger societal-level attitudes unknown. The present study investigated societal-level disapproval of marijuana use defined by birth cohort or by time-period. DESIGN Combined analysis of nationally representative annual surveys of secondary school students in the United States conducted from 1976 to 2007 as part of the Monitoring the Future study. SETTING In-school surveys completed by adolescents in the United States. PARTICIPANTS A total of 986 003 adolescents in grades 8, 10 and 12. MEASUREMENTS Main predictors included the percentage of students who disapproved of marijuana in each birth cohort and time-period. Multi-level models with individuals clustered in time-periods of observation and birth cohorts were modeled, with past-year marijuana use as the outcome. FINDINGS Results indicated a significant and strong effect of birth cohort disapproval of marijuana use in predicting individual risk of marijuana use, after controlling for individual-level disapproval, perceived norms towards marijuana and other characteristics. Compared to birth cohorts in which most (87-90.9%) adolescents disapproved of marijuana use, odds of marijuana use were 3.53 times higher in cohorts where fewer than half (42-46.9%) disapproved (99% confidence interval: 2.75, 4.53). CONCLUSIONS Individuals in birth cohorts that are more disapproving of marijuana use are less likely to use, independent of their personal attitudes towards marijuana use. Social norms and attitudes regarding marijuana use cluster in birth cohorts, and this clustering has a direct effect on marijuana use even after controlling for individual attitudes and perceptions of norms.