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Inequalities in mortality during and after restructuring of the New Zealand economy: repeated cohort studies

BMJ 2008; 336 doi: https://doi.org/10.1136/bmj.39455.596181.25 (Published 14 February 2008) Cite this as: BMJ 2008;336:371
  1. Tony Blakely, research professor1,
  2. Martin Tobias, principal adviser2,
  3. June Atkinson, senior analyst and team leader1
  1. 1Health Inequalities Research Programme, University of Otago, Wellington, PO Box 7343, Wellington, New Zealand
  2. 2Epidemiology, Public Health Intelligence, Ministry of Health, PO Box 5013, Wellington, New Zealand
  1. Correspondence to: T Blakely tony.blakely{at}otago.ac.nz
  • Accepted 19 November 2007

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.

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.

Footnotes

  • Ken Huang and Li-Chia Yeh (Public Health Intelligence, Ministry of Health) assisted with statistical analysis. Diana Sarfati, Caroline Shaw, and Kristie Carter (University of Otago), and Jackie Fawcett (Accident Compensation Corporation) commented on the manuscript. This paper is published with the approval of the deputy director general (public health), New Zealand Ministry of Health. Opinions are the authors’ own and do not necessarily reflect ministry policy advice. Access to the data used in this study was provided by Statistics New Zealand under conditions designed to give effect to the security and confidentiality provisions of the Statistics Act 1975. The results presented in this study are the work of the authors, not Statistics New Zealand.

  • Contributors: TB and MT jointly conceived the paper and contributed to design, interpretation, and preparation of drafts of the paper. JA led the statistical analyses and contributed to drafting of the paper. TB is guarantor.

  • Funding: Health Research Council of New Zealand and Ministry of Health.

  • Competing interests: None declared.

  • Ethical approval: Wellington regional ethics committee.

  • Provenance and peer review: Not commissioned; externally peer reviewed.

  • Accepted 19 November 2007
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