Minimum purchasing age for alcohol and traffic crash injuries among 15- to 19-year-olds in New Zealand.

Abstract: 

Objectives. In 1999, New Zealand lowered the minimum purchasing age for alcohol from 20 to 18 years. We tested the hypothesis that this increased traffic crash injuries among 15- to 19-year-olds. Methods. Poisson regression was used to compute incidence rate ratios for the after to before incidence of alcohol-involved crashes and hospitalized injuries among 18- to 19-year-olds and 15- to 17-year-olds (20- to 24-year-olds were the reference). Results. Among young men, the ratio of the alcohol-involved crash rate after the law change to the period before was 12% larger (95% confidence interval [CI]= 1.00, 1.25) for 18- to 19-year-olds and 14% larger (95% CI= 1.01, 1.30) for 15- to 17-year-olds, relative to 20- to 24-year-olds. Among young women, the equivalent ratios were 51% larger (95% CI = 1.17, 1.94) for 18- to 19-year-olds and 24% larger (95% C1=0.96, 1.59) for 15- to 17-year-olds. A similar pattern was observed for hospitalized injuries. Conclusions. Significantly more alcohol-involved crashes occurred among 15- to 19-year-olds than would have occurred had the purchase age not been reduced to 18 years. The effect size for 18- to 19-year-olds is remarkable given the legal exceptions to the pre-1999 law and its poor enforcement.