Background: The Rutgers Alcohol Problem Index (RAPI) is widely used to assess adolescent drinking-related problems. We asked how well RAPI, administered in late adolescence, predicts alcohol diagnoses at age 25 in a 7-year follow-up.
Methods: At age 18, a population-based sample of Finnish twins completed RAPI by postal questionnaire; 597 (300 male) twins, from pairs discordant and concordant for age 18 RAPI scores, were interviewed at age 25 with the SSAGA, yielding DSM-IIIR diagnoses. Polychoric correlations between RAPI and alcohol diagnoses and symptoms, the area under the response operator characteristic (ROC) curve, and the odds ratio of outcome diagnosis per unit change in adolescent RAPI were analyzed. Twin pairs discordant for both adolescent RAPI and adult diagnoses permitted within-family replications for the full sample and separately by sex.
Results: Nearly half the interviewed twins met diagnostic criteria for alcohol dependency (46.2%) or abuse (1.5%). Age 18 RAPI scores significantly correlated with diagnoses (0.52) and symptom counts (0.55). ROC analysis found a 74% probability that adolescent RAPI scores will be higher among those with an alcohol diagnosis at age 25 than for those without. The odds ratio of outcome alcohol diagnosis per unit increase in adolescent 18 RAPI exceeded 10.0. Within-family comparisons of 117 twin pairs discordant for both age 18 RAPI and age 25 alcohol diagnoses replicated the between-family associations. In both between-family and within-family analyses, RAPI was more predictive of alcohol diagnoses among females.
Conclusions: Our results offer evidence, including that from informative comparisons of co-twins discordant for both predictor and outcome, that RAPI scores in late adolescence robustly predict alcohol diagnoses in early adulthood. Accordingly, our results also provide new evidence that one pathway to problem drinking in early adulthood is a direct one from problem drinking in adolescence.