BMJ 2002;324:1-2 ( 5 January ) <http://bmj.com/cgi/content/full/324/7328/1>
Editorials
Income inequality and population health
Evidence favouring a negative correlation between income inequality and life expectancy has disappeared
In 1992, the BMJ published a now famous paper showing a strong negative correlation between income inequality and life expectancy. Among nine Western industrialised countries those which had less income inequality seemed to have higher life expectancy.1 A few years later this was replicated in analyses looking at income inequality and mortality in states within the United Statesanalyses which seemed more secure because of having more and better quality data. 2 3 These findings, which suggested that income inequality is bad for the health of the whole population and not only for those with the lowest incomes, were seen to have important implications. Reducing the inequality would be in everyone's interest, including those with higher incomes.
A novel area of research was born, adding new perspectives to conventional studies of health inequalities. These had tended to focus on relations between socioeconomic factors and health of the individual, while the findings on income inequality suggested that contextual effects of inequality might be just as important. Considerable dissent, however, emerged on the explanation of these effects. Some favoured softer psychosocial pathways (for example through feelings of relative deprivation, or disruption of social cohesion) while others favoured harder material pathways (for example through underinvestment in public resources).4-6 Support was found for some of these mechanisms, which are also important in their own right, and the debate on income inequality versus mortality acted as a strong stimulus for further work on factors such as social cohesion and social capital.7 Although most of the papers dealt with mortality or life expectancy as measures of the health of the population, results from geographical analyses within the United States suggested possible effects of income inequality on self rated health as well.8
All along, however, critical questions were being asked about the quality and interpretation of the data. In an early exchange, serious criticisms of the selection of countries, the quality of the data, and the lack of control for confounding in the BMJ paper of 1992 were only half countered. 9 10 Although many aspects of this debate are still unresolved, it has recently become clear that the findings in that paper were an artefact of the selection of countries. Now that good data on income inequality have become available for 16 western industrialised countries, the association between income inequality and life expectancy has disappeared.
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