Is Health Made or Bought? New Evidence on the Roles of Work and Income as Determinants of Health

1. Is Health Made or Bought? New Evidence on the Roles of Work and Income as Determinants of Health • the debates: psycho-social or neo-material; role of income inequality? • new data: 1991 Census mortality linkage • method: examine gradients in detail Michael Wolfson, Statistics Canada with Philippe Fines, Geoff Rowe, and Russell Wilkins and financial support from the Canadian Population Health Initiative of CIHI CPHA June 2008

2. Alternate Hypotheses • background: there is a significant and pervasive gradient in health with socio-economic status • over-simplified statement of alternate hypotheses: • health is “made” – the main factor determining the gradient is individuals’ rank in society, particularly the psycho-social aspects of their position in paid work • health is “bought” – the main factor is purchasing power / command over resources CPHA June 2008

3. Brief Review of Literature (I)(Wilkinson, BMJ, 1997) • “Is the health disadvantage of the least well off part of the population mainly a reflection of the direct physiological effects of lower absolute material standards (of bad housing, poor diets, inadequate heating, and air pollution), or is it more a matter of the direct and indirect effects of differences in psychosocial circumstances associated with social position – of where you stand in relation to others? … • “Evidence … suggests that the psychosocial effects of social position account for the larger part of health inequalities.” CPHA June 2008

4. Brief Review of Literature (II)(Siegrist and Marmot, SSM, 2004) • “It is unlikely that there will be a single explanation of social inequalities in health. … one explanatory framework (is) exposure to adverse psychosocial environments during midlife, particularly at work. • “We argue that exposure to an adverse psychosocial environment, in terms of job tasks, defined by high demands and low control and/or by effort–reward imbalance, elicits sustained stress reactions with negative long-term consequences for health.” CPHA June 2008

5. Brief Review of Literature (III)(Lynch, Kaplan et al., BMJ, 2000) • “The neo-material interpretation says that health inequalities result from the differential accumulation of exposures and experiences that have their sources in the material world. … • “Under a neo-material interpretation, the effect of income inequality on health reflects a combination of negative exposures and lack of resources held by individuals, along with systematic underinvestment across a wide range of human, physical, health, and social infrastructure.” CPHA June 2008

6. Marmot et al. Theory Brunner and Marmot, OUP, 2006 CPHA June 2008

7. Note on Income Inequality (I) • there would be no observable gradient if everyone had the same SES • hence income inequality (i.e. variation in incomes, and SES more generally) is necessary to observe gradients (i.e. health inequalities) in the first place • the gradient itself is a relationship at the individual level – between income and health • there are also many analyses at the “meso” level of the relationship between inequality and health CPHA June 2008

8. (5 countries and their cities) Ross et al., 2002 CPHA June 2008

9. n.b. both ecological measures

10. Note on Income Inequality (II) • inequality is a property of population groups (e.g. cities, countries), not individuals, and is sometimes correlated with mortality rates, also a meso level property • the SES gradient in health is an individual-level relationship • one approach: is there, over and above an individual level SES gradient, an independent role for meso level characteristics • but Wilkinson, “Rather than income inequality being about something different, it is telling us more about the effect of class on health…” (personal communication) • “All societies … have hierarchies. Yet the magnitude of the social gradient in health varies among societies and within a society over time.” (Marmot, JAMA 2006) CPHA June 2008

11. U.S. Income Distribution and Income Gradient, 1991 (Wolfson et al., BMJ, 1999) CPHA June 2008

12. Income Inequality and the Shape of the Mortality Gradient – Are They Linked? relative risk (gradients) or population (%) “Swedish” Income Distribution “UK” Income Distribution “Swedish” Mortality Gradient “UK” Mortality Gradient income CPHA June 2008

13. Note on Dual Labour Markets • long history in labour economics re dual or segmented labour market theories • essential (simplified) idea – labour market is segmented with two groups of workers • permanents – have stable career-oriented jobs, generally in large organizations with good internal promotion possibilities • temporaries – hold a sequence of short-term unstable jobs, frequently unemployed CPHA June 2008

14. From Theory to Empirical Test: Hypothesis Restated • if job circumstances (especially demand-control and effort-reward imbalances, and civil service “grade” per Whitehall) are the main drivers of the gradient, • then a dollar of own wage income should be a stronger marker of the relevant aspects of social position than a dollar of income from any other source CPHA June 2008

15. Alternative Measures of Income – own wages vs all other household income CPHA June 2008

16. Overview of 1991 Census – Mortality Linkage • Data sources • 1991 census (+post-censal disability survey, HALS) • 1991-2001 death records (CMDB) • 15% sample of population aged 25+ • ≈ 3 out of 4 long-form census households • ≈ 2.7 million records for individuals • Follow-up for deaths 1991-2001 • ≈ 28 million person-years at risk • ≈ 260,000 deaths CPHA June 2008

17. Comparison of Life Table and 1991 Census Cohort Survival Rates age groups followed deaths followed CPHA June 2008

18. 10 Year Relative Mortality Hazards by Sex and Type of Income ($000s) 19.5% 36.3% males females 49.3% 91.3% income $000s income $000s reference income group, relative risk = 1 CPHA June 2008

19. population joint distns males own wages males all other household income females females own wages CPHA June 2008

20. Contour Plots of Joint Distributions of Own Wages and All Other Household Income ($000s), Males and Females own wages females males all other household income CPHA June 2008

21. Contour Plots of Joint Distributions of Own Wages and All Other Household Income ($000s), Males and Females own wages females males all other household income CPHA June 2008

22. Jointly Estimated Gradients females males income $000s income $000s reference income group, relative risk = 1 CPHA June 2008

23. Contour Plot of Relative Mortality Hazard if “Health is (Entirely) Made” own wage income other household income CPHA June 2008

24. Contour Plot of Relative Mortality Hazard if “Health is Bought” own wage income other household income CPHA June 2008

25. Estimated and Lightly Smoothed Contour Plots of Relative Mortality Hazards: own wages on vertical axis, other household income on horizontal ($000s) females males CPHA June 2008

26. Summary Interpretation of Results (I) • IF dollar amounts of wages are a good proxy for workplace psycho-social factors, • then these factors have at most a small incremental effect on mortality risks among the working-age population • over and above the effects of factors which are proxied by money income in general CPHA June 2008

27. Summary Interpretation of Results (II) • there are significant male-female differences • workplace factors, to the extent proxied by own wages, are more important for men compared to factors proxied by other household income • own wages are less important for women – though note that the main component in other household income for women is husbands’ wages CPHA June 2008

28. Summary Interpretation of Results (III) • note that (in fact) this is not a general test of psycho-social vs neo-material theories • the apparent protective effects of an extra dollar of other household income could still be a reflection of, or a marker for, an unobserved psycho-social factor • but if there are such psycho-social factors, they must be operating via pathways more general and pervasive than those unique to the work place CPHA June 2008

29. Concluding Thoughts: General general implication: health is more likely bought than made i.e. impacts of workplace psycho-social factors are at most small relative to “what money in general buys or reflects” at least in Canada, perhaps as compared to the UK this analysis is just a beginning re exploiting full potential of this 1991 census–mortality linkage with 28 million person-years of follow-up CPHA June 2008

30. Concluding Thoughts: Caveats and (Exciting!) Next Steps • need to distinguish different household types - e.g. couples, lone parents, 3+ adult households • add other covariates such as educational attainment, occupation / industry, ethnicity, … • begin exploring conjectures re dual labour markets • should have adequate statistical power for multi-level analysis – especially [ income inequality ↔ mortality ] versus [ unemployment ↔ mortality ] results, and (reframed) Wilkinson hypothesis CPHA June 2008