Citation

Blakely TA, Tobias M, Atkinson J. Br. Med. J. BMJ 2008; 336(7640): 371-375.

Affiliation

Health Inequalities Research Programme, University of Otago, Wellington, PO Box 7343, Wellington, New Zealand.

Copyright

(Copyright © 2008, BMJ Publishing Group)

DOI

10.1136/bmj.39455.596181.25

PMID

18218998

PMCID

PMC2244751

Abstract

OBJECTIVES: To determine whether disparities between income and mortality changed during a period of major structural and macroeconomic reform and to estimate the changing contribution of different diseases to these disparities.

DESIGN: Repeated cohort studies.

DATA SOURCES: 1981, 1986, 1991, 1996, and 2001 censuses linked to mortality data. Population Total New Zealand population, ages 1-74 years.

METHODS: Mortality rates standardised for age and ethnicity were calculated for each census cohort by level of household income. Standardised rate differences and rate ratios, and slope and relative indices of inequality (SII and RII), were calculated to measure disparities on both absolute and relative scales.

RESULTS: All cause mortality rates declined over the 25 year study period in all groups stratified by sex, age, and income, except for 25-44 year olds of both sexes on low incomes among whom there was little change. In all age groups pooled, relative inequalities increased from 1981-4 to 1996-9 (RIIs increased from 1.85 (95% confidence interval 1.67 to 2.04) to 2.54 (2.29 to 2.82) for males and from 1.54 (1.35 to 1.76) to 2.12 (1.88 to 2.39) for females), then stabilised in 2001-4 (RIIs of 2.60 (2.34 to 2.89) and 2.18 (1.93 to 2.45), respectively). Absolute inequalities were stable over time, with a possible fall from 1996-9 to 2001-4. Cardiovascular disease was the major contributor to the observed disparities between income and mortality but decreased in importance from 45% in 1981-4 to 33% in 2001-4 for males and from 50% to 29% for females. The corresponding contribution of cancer increased from 16% to 22% for males and from 12% to 25% for females.

Rates of unintentional injury tended to fall in all income groups, with moderate and persistent disparities (increasing in relative terms for males). Suicide rates by income group were unstable over time for females, but increased over time in all income groups for males up to 1996-9 (more so for the low income group), then fell for all income groups from 1996-9 to 2001-4.

CONCLUSIONS: During and after restructuring of the economy disparities in mortality between income groups in New Zealand increased in relative terms (but not in absolute terms), but it is difficult to confidently draw a causal link with structural reforms. The contribution of different causes of death to this inequality changed over time, indicating a need to re-prioritise health policy accordingly.

An important and concerning finding is the widening income-mortality disparity among young adults (25-44 years), a consequence of little if any improvement in mortality rates among the low income group. Suicide and unintentional injury made substantial contributions to widening inequality between income and mortality in this age group -- both causes with plausibly short time lags from social exposure to outcome. This finding suggests that underprivileged young adults are being left behind in New Zealand society and identifies an issue requiring urgent research and policy attention.

Language: en