Background: A prevailing epidemiological theory about drug use occurrence among secondary school students is that trends in perceived risk of drug-related harms can drive use. If so, cannabis risk perceptions during one school year should predict newly incident cannabis use in the same school the following year. We aimed to study trends in incidence and epidemiological clustering of cannabis use among United States (US) 12th-graders, and a novel prediction that incidence in school-year 't' is influenced by school-specific cannabis risk perceptions (CRP) of 12th-graders a year prior at 't-1'.
Methods: US schools sampled each year from 1976 to 2013 (∼130 schools per year) yielded an annual nationally representative sample of ∼15-16,000 12th-graders with questionnaire assessments. Analyses involved Alternating Logistic Regressions (ALR) to study trends in school-level clustering and slopes that estimate the degree to which CRP levels at 't-1' might predict newly incident cannabis use at 't'.
Results: School-level CRP levels at 't-1' predict newly incident cannabis use in the next year's 12th-grade class. For each unit CRP increment, the next year's class shows tangibly reduced incidence of starting to use cannabis (overall odds ratio, OR = 0.10; 95% CI: 0.03, 0.33). Within-school clustering of newly incident cannabis smoking also can be seen (e.g., pairwise odds ratio, PWOR = 1.11; 95% CI: 1.07, 1.15).
Conclusions: Programmatic manipulation of perceived risk in one year's senior class via public health/school alliances might dampen the subsequent risk of newly incident cannabis use in the next year's class.
Keywords: Adolescents; Cannabis; Clustering; Epidemiology; Incidence; Marijuana; Perception; Risk.
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