Kypros Kypri

School of Medicine and Public HealthUniversity of Newcastle, Australia

Injury Prevention Research UnitDepartment of Preventive & Social Medicine,

University of Otago, New Zealand

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

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

Co-investigators

Patrick McElduffUniversity of Newcastle, Australia

Gabrielle Davie, Jennie Connor, John LangleyUniversity of Otago, New Zealand

Funding: Health Research Council Project Grant 2012-15

BackgroundBackground• 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)

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

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

Logic framework for reviews of interventions to reduce alcohol-impaired driving

6

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

AimsAims

• 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)

Causal modelCausal model

MethodsMethods

• 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/dL law from August 2011)

PatientsPatients• 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

Māori ethnicityMāori 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

AnalysisAnalysis

• 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

Results – Males (all)Results – Males (all)Age group

(years)

Period:

December to

November

Mean

assaults

per year

Population

(per year)

Rate

(per

10,000

persons per

year)

Within age

group

Post/Pre IRR

(95% CI)

 

Effect estimate:

Ratio of IRRs (95%

CI):

Target and trickle

down groups relative

to 20-21 year-olds

 

15-17

(“Trickle down”)

Pre: 1995-1999 133 83453 15.9 1 1

Post 1: 1999-2003 199 87531 22.8 1.43 (1.28 to 1.60) 1.28 (1.10 to 1.49)

Post 2: 2003-2007 234 97036 24.1 1.52 (1.36 to 1.69) 1.25 (1.08 to 1.45)

Post 3: 2007-2011 214 96858 22.0 1.39 (1.24 to 1.54) 1.04 (0.90 to 1.21)

 

18-19

(Target)

Pre: 1995-1999 166 54726 30.3 1 1

Post 1: 1999-2003 211 57422 36.5 1.20 (1.09 to 1.33) 1.08 (0.93 to 1.24)

Post 2: 2003-2007 274 61698 44.4 1.46 (1.33 to 1.61) 1.21 (1.05 to 1.39)

Post 3: 2007-2011 324 67319 48.2 1.59 (1.45 to 1.74) 1.20 (1.05 to 1.37)

 

20-21

(Control)

Pre: 1995-1999 170 53735 31.5 1

1

Post 1: 1999-2003 200 56734 35.2 1.12 (1.01 to 1.24)

Post 2: 2003-2007 229 60008 38.1 1.21 (1.09 to 1.33)

Post 3: 2007-2011 281 67196 41.9 1.33 (1.21 to 1.46)

Results – Females (all)Results – Females (all)Age group

(years)

Period:

December to

November

Mean

assaults

per year

Population

(per year)

Rate

(per

10,000 persons

per year)

Within age group

Post/Pre IRR

(95% CI)

 

Effect estimate

Ratio of IRRs (95% CI):

Target and trickle down groups

relative to 20-21 year-olds

 

15-17

(“Trickle

down”)

Pre: 1995-1999 29.8 79658 3.7 1 1

Post 1: 1999-2003 38.0 84211 4.5 1.21 (0.95 to 1.54) 0.82 (0.58 to 1.15)

Post 2: 2003-2007 51.3 93529 5.5 1.47 (1.17 to 1.84) 0.96 (0.69 to 1.33)

Post 3: 2007-2011 56.0 92071 6.1 1.63 (1.30 to 2.03) 0.79 (0.58 to 1.09)

 

18-19

(Target)

Pre: 1995-1999 26.0 53142 4.9 1 1

Post 1: 1999-2003 37.3 55951 6.7 1.36 (1.06 to 1.75) 0.92 (0.65 to 1.30)

Post 2: 2003-2007 43.0 59847 7.2 1.47 (1.15 to 1.87) 0.96 (0.68 to 1.35)

Post 3: 2007-2011 69.3 63970 10.8 2.21 (1.78 to 2.77) 1.08 (0.78 to 1.48)

 

20-21

(Control)

Pre: 1995-1999 27.0 53055 5.1 1 1Post 1: 1999-2003 41.8 55355 7.5 1.48 (1.16 to 1.89)

Post 2: 2003-2007 46.0 59032 7.8 1.53 (1.21 to 1.94)

Post 3: 2007-2011 66.5 63684 10.4 2.05 (1.64 to 2.57)

Results – Māori MalesResults – Māori MalesAge group

 

Period*

 

Mean

assaults

per year

Population

(per year)

Rate

(per

10,000 persons

per year)

Within age group

Post/Pre IRR

(95% CI)

 

Effect estimate:

Ratio of IRRs

(95% CI):

Target and

trickle down

groups relative

to 20-21 year-

olds

 

15-17

years

Pre: 1995-1999 32 16640 18.9 1 1

Post 1: 1999-

2003 5717955

31.71.68 (1.35, 2.01) 1.13 (0.82, 1.55)

Post 2: 2003-

2007 6420563

30.91.63 (1.32, 2.02) 1.03 (0.76, 1.41)

Post 3: 2007-

2011 6421115

30.41.61 (1.30, 1.99) 0.85 (0.63, 1.15)

 

18-19

years

Pre: 1995-1999 38 10893 34.9 1 1

Post 1: 1999-

2003 4710850

43.31.24 (1.00, 1.54) 0.83 (0.61, 1.14)

Post 2: 2003-

2007 6712123

55.51.59 (1.30, 1.94) 1.01 (0.74, 1.36)

Post 3: 2007-

2011 8413588

61.81.77 (1.46, 2.15) 0.93 (0.70, 1.25)

 

20-21

years

(Control)

Pre: 1995-1999 30 10075 29.5 1

1

Post 1: 1999-

2003 449900

43.91.49 (1.18, 1.88)

Post 2: 2003-

2007 4910453

46.61.58 (1.26, 1.98)

Post 3: 2007-

2011 6912225

56.01.90 (1.53, 2.35)

Results – Māori FemalesResults – Māori FemalesAge group

 

Period*

 

Mean

assaults

per year

Population

(per year)

Rate

(per

10,000 persons

per year)

Within age group

Post/Pre IRR

(95% CI)

 

Effect estimate:

Ratio of IRRs

(95% CI):

Target and

trickle down

groups relative

to 20-21 year-

olds

 

15-17

years

Pre: 1995-1999 12 16390 7.0 1 1

Post 1: 1999-2003 13 17880 7.4 1.06 (0.71, 1.57) 0.60 (0.35, 1.03)

Post 2: 2003-2007 24 20378 11.5 1.64 (1.16, 2.34) 1.09 (0.65, 1.82)

Post 3: 2007-2011 28 19888 13.8 1.97 (1.40, 2.78) 0.78 (0.48, 1.27)

 

18-19

years

Pre: 1995-1999 11 11035 9.5 1 1

Post 1: 1999-2003 16 10873 14.9 1.57 (1.07, 2.32) 0.89 (0.52, 1.53)

Post 2: 2003-2007 18 12393 14.7 1.55 (1.06, 2.26) 1.02 (0.60, 1.75)

Post 3: 2007-2011 29 13210 22.0 2.31 (1.62, 3.28) 0.92 (0.56, 1.50)

 

20-21

years

(control)

Pre: 1995-1999 11 10458 10.3 1

1Post 1: 1999-2003 19 10203 18.1 1.8 (1.21, 2.57)

Post 2: 2003-2007 17 11085 15.6 1.51 (1.03, 2.22)

Post 3: 2007-2011 32 12358 25.9 2.52 (1.78, 3.56)

SummarySummary

• 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

LimitationsLimitations• 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)

In relation to Māori 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)

ImplicationsImplications• 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

22Otago Daily Times: May 2004

Minister of Justice

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).