Effects of Lowering the Minimum Alcohol Purchasing Age on Weekend Assaults Resulting in Hospitalization in New Zealand

Objectives. We estimated the effects on assault rates of lowering the minimum alcohol purchasing age in New Zealand from 20 to 18 years. We hypothesized that the law change would increase assaults among young people aged 18 to 19 years (the target group) and those aged 15 to 17 years via illegal sales or alcohol supplied by older friends or family members. Methods. Using Poisson regression, we examined weekend assaults resulting in hospitalization from 1995 to 2011. Outcomes were assessed separately by gender among young people aged 15 to 17 years and those aged 18 to 19 years, with those aged 20 and 21 years included as a control group. Results. Relative to young men aged 20 to 21 years, assaults increased significantly among young men aged 18 to 19 years between 1995 and 1999 (the period before the law change), as well as the postchange periods 2003 to 2007 (incidence rate ratio [IRR] = 1.21; 95% confidence interval [CI] = 1.05, 1.39) and 2008 to 2011 (IRR = 1.20; 95% CI = 1.05, 1.37). Among boys aged 15 to 17 years, assaults increased during the postchange periods 1999 to 2003 (IRR = 1.28; 95% CI = 1.10, 1.49) and 2004 to 2007 (IRR = 1.25; 95% CI = 1.08, 1.45). There were no statistically significant effects among girls and young women. Conclusions. Lowering the minimum alcohol purchasing age increased weekend assaults resulting in hospitalization among young males 15 to 19 years of age.