What would it take to eradicate health inequalities? A cross-sectional study using routine administrative data

Abstract

BackgroundPhelan and Link argue that socioeconomic status is a fundamental cause of mortality inequalities, hypothesising that any fundamental cause (other candidates include racism and stigma) will have three essential features: (1) will be associated with many disease outcomes; (2) will affect outcomes through a range of intervening mediators; and (3) will persistently display health gradients despite substitution of new for old mediators, such as persistent gradient in all-cause mortality despite change from infectious to non-communicable disease risk factors. They further propose that fundamental causes probably operate via differential access to many resources, which can be variously used to protect and improve health, and that there should therefore be no or lesser health gradients when deployment of resources for health advantage cannot be consciously used; for example, in cases in which we know little or nothing about how to prevent or treat a fatal disease. In view of the already substantial evidence that socioeconomic status meets the first and second essential feature of a fundamental cause as defined by Phelan and Link, we set out to assess whether there is evidence of substitution in a Scottish population sample and investigate whether socioeconomic inequalities in mortality increase with increasing preventability in Scotland. MethodsUsing death certification data and census population data from 1961, 1981, 1991, and 2001, we described trends in absolute and relative inequalities for 46 causes of death for men and women across Carstairs index of deprivation deciles between 1983 and 1999 and for men aged 20–64 years across social classes for the period 1976–1999 to assess whether substitution of specific causes of mortality had occurred. Additionally, we described mortality rates within Carstairs deciles and social classes for: (1) avoidable mortality and a sample of causes of death not classified as avoidable by the Office of National Statistics and (2) four categories of death grouped according to a pre-existing, expert-established, preventability typology. The slope index of inequality (SII), which gives a single measure of the absolute difference across socioeconomic groups while accounting for the size of each socioeconomic group, was used to describe absolute inequalities trends. The relative index of inequality was calculated by dividing the SII by the mean mortality rate and was used to describe trends in relative inequalities. FindingsAlthough socioeconomic inequalities in mortality decreased in both absolute and relative terms for certain causes of death (eg, tuberculosis and rheumatic heart disease for women), they increased over the same time period for others (eg, alcohol-related mortality and suicide). New socioeconomic gradients also emerged for many specific causes of death (eg, malignant melanoma, mortality associated with perinatal complications, and colorectal cancer). There was a clear socioeconomic gradient for avoidable mortality but not for non-avoidable mortality. Relative inequalities seemed to be directly proportional to preventability (appendix). InterpretationSocioeconomic status exhibits Phelan and Link's proposed features of a fundamental cause of disease in Scotland, being associated with several causes of death mediated by a range of intermediate mechanisms and with evidence of substitution during the observation period. Weaknesses of this work include the small numbers of deaths for some specific causes; the inclusion of a small number of non-avoidable causes of death; the use of the 1991 Carstairs index throughout; and possible numerator and denominator mismatch for social class estimates. The first of these potentially limits the reliability of some findings, and the remainder introduce potential bias. This study suggests that continuing to focus on controlling individual intermediate mediators such as tobacco will ultimately fail to eradicate health inequalities and that sustained reduction and prevention will only be achieved by addressing underlying inequalities in income, wealth, and power. FundingNone.