摘要：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% CI=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. It has been 30 years since the state of Alabama reduced its minimum legal drinking age from 20 to 18 years. 1 Alabama was the last of 29 states of the United States to do so in the period 1970 to 1975 in line with the reduction in voting age laws toward the end of the Vietnam War. 1 All 10 Canadian provinces 1 and 3 Australian states 2 passed similar legislation in this period. Several studies on the effects of those legislative changes reported substantial increases in road traffic crashes involving persons aged 15 to 20 years. In their meta-analytic review, Shults et al. 3 found that lowering the minimum legal drinking age produced a median increase of 10% in youthful crash involvements. Such harmful effects were observed in all 3 countries in which the minimum legal drinking age was reduced. Notably, increased crash involvements were observed among 15- to 17-year-olds (i.e., in persons younger than the age of the target group—so-called trickle-down effects), although the effects were inconsistent across studies. 3 Research evidence suggests that persons in the age group bordering the minimum legal drinking age are able to purchase alcohol or obtain it from friends and siblings. 4 , 5 As the research evidence came to be harnessed by public health advocates and citizens groups, several “early adopter” states passed laws in the late 1970s and early 1980s increasing the minimum legal drinking age. 1 Evaluations of these changes showed reductions in alcohol-involved traffic crashes. Consistent with the research evidence, the US federal government passed the Uniform Drinking Age Act in 1984, which provided for withholding a portion of a state’s federal highway construction funds for failure to enact a law requiring a minimum legal drinking age of 21. By 1988, all 50 states and the District of Columbia had a minimum legal drinking age of 21, creating a series of natural experiments that provided further opportunity for researchers to quantify the health effects of minimum legal drinking age laws. In their review of 17 studies from states that raised the minimum legal drinking age, Shults et al. 3 estimated average reductions in underage crash involvements of 16%. In addition to the consistent inverse relation between the minimum legal drinking age and traffic crash involvement across jurisdictions are observations of reduced heavy drinking in those exposed to a lowered minimum legal drinking age 6 and research showing that stricter enforcement of the minimum legal drinking age is associated with greater reductions in harm. 4 No traffic safety policy, with the possible exception of motorcycle safety helmet laws, has more evidence for its effectiveness than do the minimum legal drinking age laws. Nevertheless, pressure continues in the United States, particularly from liquor industry interests, to reduce minimum legal drinking ages. Notably, at least 5 of the 50 states currently have provisions to reduce the minimum legal drinking age automatically if Congress were to repeal the Uniform Drinking Age Act. Perhaps surprisingly, given the strength and volume of evidence published in the 1980s and 1990s, the New Zealand government passed the Sale of Liquor Amendment Act, which brought into effect a reduction in the minimum purchase age from 20 to 18 years, effective December 1, 1999. This occurred despite strong submissions from researchers and public health advocates for a retention of the status quo and tougher enforcement of laws pertaining to the supply of alcohol to persons younger than 20 years. 7 Notably, the changes in the minimum legal drinking age in the 1970s occurred at a time of comparatively high and increasing aggregate alcohol consumption in many developed countries. Average consumption per person aged 15 years and older reached its postwar peak between 1978 and 1982 in the United States, Canada, Australia, and New Zealand 8 before declining steadily and reaching a plateau in the late 1990s. At the time of the law change in New Zealand, aggregate consumption in these countries had declined by about 20% from its late 1970s levels. 8 Against this backdrop of reduced overall consumption, a change in young people’s drinking patterns was evident—toward heavier episodic consumption, or binge drinking. National survey data from the United States documented a 17% increase from 1993 to 2001 in binge-drinking episodes per person in the adult population. 9 Notably, among those who consumed alcohol in 2001, 51% of 18- to 20-year-olds had consumed 5 or more drinks (> 60 g ethanol) on at least one occasion in the last 30 days. 9 Also, a gender convergence in drinking behavior was seen, 10 with the proportion of young women habitually drinking to intoxication in New Zealand increasing and approaching the level for young young men. 11 , 12 The New Zealand law change created an opportunity to test the drinking age hypothesis in yet another society and in a new era. This study included an age comparison group (20- to 24-year-olds) as a control for the effects of increased availability of alcohol in supermarkets 13 and Sunday trading 14 and other coincident road safety interventions that could have affected the likelihood of road traffic crashes. Our aim was to test the hypothesis that the reduction in the minimum purchasing age increased alcohol-involved traffic crashes among 15- to 19-year-olds. We examined changes in traffic crashes involving alcohol and injuries resulting in hospitalization separately, by gender, in 3 age groups—15 to 17, 18 to 19, and 20 to 24 years—in the 4 years before and after the law change.
