Population-level predictions from cannabis risk perceptions to active cannabis use prevalence in the United States, 1991-2014.

INTRODUCTION: A mosaic of evidence links risk perceptions with drug use in adolescence, including population summaries to guide public health campaigns, as well as subject-specific estimates on preventing an adolescent's drug use by manipulating that individual's prior risk perceptions. We re-visit these issues with a public health perspective, asking whether population-level cannabis risk perceptions of school-attending adolescents at one grade level might predict cannabis use prevalence two and four grade levels later.
METHODS: From 1991 to 2014, each year's United States "Monitoring the Future" (MTF) study population included 8th-, 10th-, & 12th-graders. Two and four years later, statistically independent school samples of the same cohorts were drawn and assessed (n ~ 16,000/year). Population-level modeling estimated cannabis use prevalence at time "t" (12th-grade) regressed on that same cohort's cannabis risk perceptions as had been measured at time "t-4" (8th-grade) and time "t-2" (10th-grade).
RESULTS: Higher cannabis risk perception levels for 10th-graders predict lower cannabis use prevalence when 10th-graders have become 12th-graders (β̂=-0.12), and higher cannabis risk perception levels of 8th-graders predict lower cannabis prevalence when 8th-graders have become 10th-graders (β̂=-0.27); p-values < 0.05. Across four-year spans, the prediction is null (p-value = 0.619).
CONCLUSIONS: This within-cohort across-grade population-level prediction prompts questions for drug prevention specialists, including "Would a relatively small upward shift in a local area population's appraisal of risk perceptions be followed, two years later, by reduced population prevalence of cannabis use?" Future randomized trial designs, health education, or prevention efforts focused on altering early adolescent cannabis risk perceptions might provide the most convincing and definitive evidence.