This study sought to determine the effects on assault rates following the lowering of the minimum alcohol purchasing age in NZ from 20 to 18 years in December 1999. The study researchers examined data on weekend assaults resulting in hospitalisation throughout NZ from 1995 to 2011. Outcomes were assessed separately by gender among 3 age groups: 15–17 years, 18–19 years, and a control group consisting of 20–21-year-olds. Assault rates increased significantly among males aged 18–19 years between 1995 and 1999 (the period before the law change), as well as the postchange periods 2003–2007 (incidence rate ratio [IRR] 1.21; 95% CI, 1.05 to 1.39) and 2008–2011 (IRR 1.20; 95% CI, 1.05 to 1.37), when compared with young men aged 20–21 years. Among males aged 15–17 years, assaults increased during the postchange periods 1999–2003 (IRR 1.28; 95% CI, 1.10 to 1.49) and 2004–2007 (IRR 1.25; 95% CI, 1.08 to 1.45). There were no statistically significant effects among girls and young women.
