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. 2003 Apr;57(4):279–284. doi: 10.1136/jech.57.4.279

No association of income inequality with adult mortality within New Zealand: a multi-level study of 1.4 million 25–64 year olds

T Blakely 1, J Atkinson 1, D O'Dea 1
PMCID: PMC1732433  PMID: 12646545

Abstract

Study objective: To determine the association of regional income inequality within New Zealand with mortality among 25–64 year olds.

Design: Individual census and mortality records were linked over the 1991–94 period. Income inequality (Gini coefficients) and average household income variables were calculated for 35 regions. "Individual level" variables were sex, age, ethnicity, household income, rurality, and small area socioeconomic deprivation. Logistic regression was used for the analyses. Sensitivity analyses for the level of regional aggregation were conducted.

Participants: 1.4 million New Zealand census respondents aged 25–64 years followed up for mortality for three years.

Main results: Controlling for age, ethnicity, rurality, household income, and regional mean income, there was no association of income inequality with all cause mortality for either men (OR=1.007 for a 0.01 increase in the Gini, 95% confidence intervals 0.989 to 1.024) or women (OR=1.004, 0. 983 to 1.026). By cause of death (cancer, cardiovascular disease, unintentional injury, and suicide) there was some suggestion of a positive association for female unintentional injury (OR=1.068, 0.952 to 1.198) and suicide (OR=1.087, 0.957 to 1.234) but the 95% confidence intervals all included 1.0. Failure to control for ethnicity at the individual level resulted in some association of increasing regional income inequality with increasing mortality risk. Using fewer (n=14) or more (n=73) regional divisions did not substantially change the findings.

Conclusion: There is no convincing evidence of an association of income inequality within New Zealand with adult mortality. Previous ecological analyses within New Zealand suggesting an association of income inequality with mortality were confounded by ethnicity at the individual level. However, this study does not refute the possibility that income inequality at the national level affects health.

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Selected References

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  1. Backlund E., Sorlie P. D., Johnson N. J. The shape of the relationship between income and mortality in the United States. Evidence from the National Longitudinal Mortality Study. Ann Epidemiol. 1996 Jan;6(1):12–22. doi: 10.1016/1047-2797(95)00090-9. [DOI] [PubMed] [Google Scholar]
  2. Blakely T. A., Kennedy B. P., Glass R., Kawachi I. What is the lag time between income inequality and health status? J Epidemiol Community Health. 2000 Apr;54(4):318–319. doi: 10.1136/jech.54.4.318. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Blakely T. A., Kennedy B. P., Kawachi I. Socioeconomic inequality in voting participation and self-rated health. Am J Public Health. 2001 Jan;91(1):99–104. doi: 10.2105/ajph.91.1.99. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Blakely T. A., Woodward A. J. Ecological effects in multi-level studies. J Epidemiol Community Health. 2000 May;54(5):367–374. doi: 10.1136/jech.54.5.367. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Blakely T., Woodward A. Income inequality and mortality in Canada and the United States. Third explanation is plausible. BMJ. 2000 Dec 16;321(7275):1532–1534. [PMC free article] [PubMed] [Google Scholar]
  6. Blakely T., Woodward A., Salmond C. Anonymous linkage of New Zealand mortality and Census data. Aust N Z J Public Health. 2000 Feb;24(1):92–95. doi: 10.1111/j.1467-842x.2000.tb00732.x. [DOI] [PubMed] [Google Scholar]
  7. Blakely Tony A., Lochner Kimberly, Kawachi Ichiro. Metropolitan area income inequality and self-rated health--a multi-level study. Soc Sci Med. 2002 Jan;54(1):65–77. doi: 10.1016/s0277-9536(01)00007-7. [DOI] [PubMed] [Google Scholar]
  8. Blakely Tony, Kiro Cindy, Woodward Alistair. Unlocking the numerator-denominator bias. II: Adjustments to mortality rates by ethnicity and deprivation during 1991-94. The New Zealand Census-Mortality Study. N Z Med J. 2002 Feb 8;115(1147):43–48. [PubMed] [Google Scholar]
  9. Brodish P. H., Massing M., Tyroler H. A. Income inequality and all-cause mortality in the 100 counties of North Carolina. South Med J. 2000 Apr;93(4):386–391. [PubMed] [Google Scholar]
  10. Daly M. C., Duncan G. J., Kaplan G. A., Lynch J. W. Macro-to-micro links in the relation between income inequality and mortality. Milbank Q. 1998;76(3):315-39, 303-4. doi: 10.1111/1468-0009.00094. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Fiscella K., Franks P. Poverty or income inequality as predictor of mortality: longitudinal cohort study. BMJ. 1997 Jun 14;314(7096):1724–1727. doi: 10.1136/bmj.314.7096.1724. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Gravelle H. How much of the relation between population mortality and unequal distribution of income is a statistical artefact? BMJ. 1998 Jan 31;316(7128):382–385. doi: 10.1136/bmj.316.7128.382. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Hales S., Howden-Chapman P., Salmond C., Woodward A., Mackenbach J. National infant mortality rates in relation to gross national product and distribution of income. Lancet. 1999 Dec 11;354(9195):2047–2047. doi: 10.1016/S0140-6736(99)03763-0. [DOI] [PubMed] [Google Scholar]
  14. Kaplan G. A., Pamuk E. R., Lynch J. W., Cohen R. D., Balfour J. L. Inequality in income and mortality in the United States: analysis of mortality and potential pathways. BMJ. 1996 Apr 20;312(7037):999–1003. doi: 10.1136/bmj.312.7037.999. [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. Kawachi I., Kennedy B. P. Income inequality and health: pathways and mechanisms. Health Serv Res. 1999 Apr;34(1 Pt 2):215–227. [PMC free article] [PubMed] [Google Scholar]
  16. Kennedy B. P., Kawachi I., Glass R., Prothrow-Stith D. Income distribution, socioeconomic status, and self rated health in the United States: multilevel analysis. BMJ. 1998 Oct 3;317(7163):917–921. doi: 10.1136/bmj.317.7163.917. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Kennedy B. P., Kawachi I., Prothrow-Stith D. Income distribution and mortality: cross sectional ecological study of the Robin Hood index in the United States. BMJ. 1996 Apr 20;312(7037):1004–1007. doi: 10.1136/bmj.312.7037.1004. [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. Lochner K., Pamuk E., Makuc D., Kennedy B. P., Kawachi I. State-level income inequality and individual mortality risk: a prospective, multilevel study. Am J Public Health. 2001 Mar;91(3):385–391. doi: 10.2105/ajph.91.3.385. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Lynch J. W., Kaplan G. A., Pamuk E. R., Cohen R. D., Heck K. E., Balfour J. L., Yen I. H. Income inequality and mortality in metropolitan areas of the United States. Am J Public Health. 1998 Jul;88(7):1074–1080. doi: 10.2105/ajph.88.7.1074. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Lynch J. W., Smith G. D., Kaplan G. A., House J. S. Income inequality and mortality: importance to health of individual income, psychosocial environment, or material conditions. BMJ. 2000 Apr 29;320(7243):1200–1204. doi: 10.1136/bmj.320.7243.1200. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Lynch J. Income inequality and health: expanding the debate. Soc Sci Med. 2000 Oct;51(7):1001–1010. doi: 10.1016/s0277-9536(00)00080-0. [DOI] [PubMed] [Google Scholar]
  22. Lynch J., Smith G. D., Hillemeier M., Shaw M., Raghunathan T., Kaplan G. Income inequality, the psychosocial environment, and health: comparisons of wealthy nations. Lancet. 2001 Jul 21;358(9277):194–200. doi: 10.1016/S0140-6736(01)05407-1. [DOI] [PubMed] [Google Scholar]
  23. Osler Merete, Prescott Eva, Grønbaek Morten, Christensen Ulla, Due Pernille, Engholm Gerda. Income inequality, individual income, and mortality in Danish adults: analysis of pooled data from two cohort studies. BMJ. 2002 Jan 5;324(7328):13–16. doi: 10.1136/bmj.324.7328.13. [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Ross N. A., Wolfson M. C., Dunn J. R., Berthelot J. M., Kaplan G. A., Lynch J. W. Relation between income inequality and mortality in Canada and in the United States: cross sectional assessment using census data and vital statistics. BMJ. 2000 Apr 1;320(7239):898–902. doi: 10.1136/bmj.320.7239.898. [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Salmond C., Crampton P., Sutton F. NZDep91: A New Zealand index of deprivation. Aust N Z J Public Health. 1998 Dec;22(7):835–837. doi: 10.1111/j.1467-842x.1998.tb01505.x. [DOI] [PubMed] [Google Scholar]
  26. Shibuya Kenji, Hashimoto Hideki, Yano Eiji. Individual income, income distribution, and self rated health in Japan: cross sectional analysis of nationally representative sample. BMJ. 2002 Jan 5;324(7328):16–19. doi: 10.1136/bmj.324.7328.16. [DOI] [PMC free article] [PubMed] [Google Scholar]
  27. Soobader M. J., LeClere F. B. Aggregation and the measurement of income inequality: effects on morbidity. Soc Sci Med. 1999 Mar;48(6):733–744. doi: 10.1016/s0277-9536(98)00401-8. [DOI] [PubMed] [Google Scholar]
  28. Stanistreet D., Scott-Samuel A., Bellis M. A. Income inequality and mortality in England. J Public Health Med. 1999 Jun;21(2):205–207. doi: 10.1093/pubmed/21.2.205. [DOI] [PubMed] [Google Scholar]
  29. Sturm Roland, Gresenz Carole Roan. Relations of income inequality and family income to chronic medical conditions and mental health disorders: national survey. BMJ. 2002 Jan 5;324(7328):20–23. doi: 10.1136/bmj.324.7328.20. [DOI] [PMC free article] [PubMed] [Google Scholar]
  30. Wilkinson R. G. Income distribution and life expectancy. BMJ. 1992 Jan 18;304(6820):165–168. doi: 10.1136/bmj.304.6820.165. [DOI] [PMC free article] [PubMed] [Google Scholar]

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