Effects of Lowering Alcohol Minimum Purchasing Age on Weekend Hospitalized Assault in New Zealand

1. Effects of lowering the alcohol minimum purchasing age on weekend hospitalised assault in New Zealand Applied Research in Crime and Justice Conference Sydney 18-19 February 2015 Kypros Kypri School of Medicine and Public Health University of Newcastle, Australia Injury Prevention Research Unit Department of Preventive & Social Medicine, University of Otago, New Zealand

2. Co-investigators Patrick McElduff University of Newcastle, Australia Gabrielle Davie, Jennie Connor, John Langley University of Otago, New Zealand Funding: Health Research Council Project Grant 2012-15

3. Background • Minimum purchasing age (MPA) reduced from 20 to 18 years in December 1999 • Previous studies show deleterious effects on traffic injury outcomes – consistent with USA, Canada, Australia 1970s and 1980s • Few studies on intentional injury • Data quality and volume are barriers • No studies of effects on Indigenous people

4. Evidence on the minimum legal drinking age (MLDA) / minimum purchase age (MPA) • During and after the Vietnam war, 29 states of the USA, 3 Canadian provinces and 3 Australian states reduced their MLDA/MPAs • By 1988 all 50 states of the USA increased their MLDAs to 21 (note the variation in laws by state) • Over 100 studies have been published on the effects of lowering and increasing the MLDA / MPA • Evidence shows an inverse relationship between the change in MLDA / MPA and levels of alcohol consumption and traffic among 18-20 year-olds

5. Logic framework for reviews of interventions to reduce alcohol-impaired driving Shults et al. Reviews of evidence regarding interventions to reduce alcohol-impaired driving. American Journal of Preventive Medicine 2001;21:66-88.

6. Shults et al. Reviews of evidence regarding interventions to reduce alcohol-impaired driving. American Journal of Preventive Medicine 2001;21:66-88.

7. Aims • Estimate effects on the target age group (18-19 years) and a younger age group (15-17 years) from “trickle down” • Estimate effects separately for males and females • Estimate effects separately for Māori (Mana Whakamārama: equal explanatory power)

8. Causal model

9. Methods • Pre-post design with age control (20-21 years) for economic and other factors affecting drinking among young people • Pre-change period: 1996-1999 (1992 0.03 g/dL law for drivers under 20) • Three four-year post-change periods: • 2000-2003 • 2004-2007 • 2008-2011 (0.00 g/dLlaw from August 2011)

10. Patients • Admitted to public hospitals (97% of acute injury cases) in NZ from 00:01 Friday to 24:00 Sunday (“weekends”) • Note: no “alcohol involvement” nor any “time of injury indicator” is routinely recorded, thus assaults between e.g., 10pm-6am cannot be identified • Cases: patients aged 15-17 or 18-19 years • Controls: patients aged 20-21 years

11. Māori ethnicity • Self-identified ethnic group mandatory in the National Minimum Data Set • Can change over time thus ethnicity data are recorded for each hospital admission • Prioritisation determined using Statistics NZ algorithm (NZ Māori highest priority code) • Ethnicity data in health sector collected in same way as Census allowing for valid population hospitalisation rate estimates

12. Analysis • Poisson regression to model change in each age group relative to the 20-21 year-olds • Exponents of fitted coefficients are equivalent to Incidence Rate Ratios (IRR) with the pre-post*age group interaction terms providing pre-post IRRs relative to the comparison age group

13. Results – Males (all)

14. Results – Females (all)

15. Results – Māori Males

16. Results – Māori Females

17. Summary • Compared with 20-21 year-old males: • assaults increased significantly among 18-19 year-old males (IRRs 1.04 to 1.21) relative to the pre-change period. • assaults increased significantly among 15-17 year-old males (IRRs 1.08 to 1.28) relative to the pre-change period • No significant effects for females (note lower incidence rates for females 1:4 ratio) • No effects detected among Māori

18. Limitations • Statistical power restricted by sensitivity of outcome indicator (some cases will not have been alcohol involved) – bias toward the null • Inferences should not be made about trends because of change in ED coding over time –not expected to differ by age and therefore would not bias effect estimate • Lack of effect for females may reflect different victim / perpetrator dynamics by gender (age gap greater for females)

19. In relation to Māori • No large effects but small effects in either direction cannot be ruled out because of small numbers • There may be differences in informal access to alcohol between Māori and non-Māori that made the MPA less important for the former • Findings underline the importance of government evaluation planning BEFORE major policy changes, especially for Māori (Mana Whakamārama)

20. Implications • The rate of serious assault is increasing in New Zealand, particularly among young people, Māori and people living in deprived areas • Contrast with trend in traffic injury • For intentional injury (assault and deliberate self-harm) we lack the countermeasures we have for traffic injury (e.g., RBT) • Increasing the MPA / MLDA should be considered for reducing assault

22. Minister of Justice Otago Daily Times: May 2004

23. Papers available on request (kypros.kypri@newcastle.edu.au) • Effects of lowering the alcohol minimum purchasing age on weekend hospitalised assault. American Journal of Public Health, 2014, 104(8) 1396-1401 • Effects of lowering the alcohol minimum purchasing age on weekend hospitalised assaults of young Māori in New Zealand. Drug & Alcohol Review (in press 2015). • Long-term effects of lowering the alcohol minimum purchasing age on traffic crash injury rates in New Zealand (under review).