Description of the cohort
describes the predictor variables at baseline. Age and gender were equally represented. Race/ethnicity and other demographic variables were broadly reflective of the US population, with 11% Black and 19% Hispanic ethnicity. Some 18% of families were low income, with 7% having incomes of $20 000 or less and 11% having income between $20 000 and $29 000/year. At baseline, the median estimated MAE from the pool of 532 movies was 4.5 h, and at T2, 11% of the respondents reported owning alcohol-branded merchandise. Friend alcohol use was reported by 23%, parental alcohol use (greater than or equal to weekly) by 23% and could obtain alcohol from home by 29% of respondents.
Description of the sample at baseline
Alcohol use in the cohort
Over the course of the study, the prevalence of tried drinking increased from 11% to 25% (). The incidence categories show data for transitions. Among never-drinkers for each 8-month observation period, 6%–8% transitioned to ever drinking and 2%–3% transitioned to binge drinking. The risk of a transition escalated for ever-drinkers, among whom 15%–24% transitioned to binge drinking and 23%–29% transitioned to 30-day binge drinking over each 8-month period.
Alcohol use and binge drinking in the cohort
Hazard model: time to onset of drinking
Crude and AHRs for time to drinking onset are reported in and compared in , where they are sorted by magnitude, with all variables scaled so the AHR >1. Four variables had AHRs >2.0: peer alcohol use, AHR=2.88 (95% CI 2.35 to 3.53), age (2.24 (1.81 to 2.77)), MAE (2.13 (1.76 to 2.57)) and sensation seeking (2.08 (1.67 to 2.59)). Other variables with statistically significant AHRs included parenting, rebelliousness, weekly spending money, alcohol availability at home, receptivity to alcohol marketing, parent alcohol use and school performance.
Crude and adjusted hazard ratios for time to onset of alcohol use
Figure 1 Adjusted hazard ratios (AHRs) for time to alcohol onset among alcohol never users (top panel) and for progression to binge drinking among alcohol experimenters (bottom panel). Each panel sorts the AHRs by size, allowing comparison of media, family, and (more ...)
The attributable fraction modelling estimated the proportion of drinking onset transitions prevented if MAE were reduced. An intervention that reduced MAE by 25% across the population would decrease drinking onset by 8% (adjusted attributable fraction (AAF)=−0.08 (−0.09, −0.07)). Eliminating MAE entirely would decrease drinking onset by 28% (AAF=−0.28 (−0.30, −0.25)).
Hazard model: time to progression to binge drinking
Results for the multivariate hazard model for transitions to binge drinking among ever-drinkers are illustrated in , with numeric values for HRs shown in . High peer alcohol use had an AHR >2 (2.80 (2.10, 3.74)) as did White race (vs Black) (2.40 (1.62, 3.56)). Variables significantly associated with progression included race and ethnicity (higher AHR for Caucasians vs Hispanic or other non-Caucasians), age, MAE (1.63 (1.20, 2.21)), extracurricular involvement, rebelliousness and receptivity to alcohol marketing. An intervention that reduced MAE by 25% across the population would reduce the proportion of adolescent drinkers transitioning to binge drinking by 6% (AAF=−0.06 (95% CI=−0.08 to −0.03)) and eliminating the exposure entirely would reduce it by 20% (AAF=−0.20 (95% CI=−0.28 to −0.13)).
Crude and adjusted hazard ratios for time to onset of binge drinking
Contrasts: time to onset versus time to progression to binge drinking
Several variables predicted both alcohol onset and progression to binge drinking—peer alcohol use, age, MAE, receptivity to alcohol marketing, and rebelliousness. In contrast, some variables played a role in alcohol onset but not binge drinking or vice versa. Notably, none of the family predictors of alcohol onset were significant predictors of progression to binge drinking. For unskilled parenting and sensation seeking, the HR was significantly higher for onset than for binge drinking by factors of 1.76 and 1.69, respectively. Race/ethnicity did not predict onset, however, White adolescents were more likely to transition to binge drinking, with the effects for African–Americans and Hispanics being significantly stronger for binge drinking than onset by factors of 2.38 and 1.42, respectively.