摘要：Objectives. We investigated whether the processes underlying the association between income inequality and population health are related to those responsible for the socioeconomic gradient in health and whether health disparities are smaller when income differences are narrower. Methods. We used multilevel models in a regression analysis of 10 age- and cause-specific US county mortality rates on county median household incomes and on state income inequality. We assessed whether mortality rates more closely related to county income were also more closely related to state income inequality. We also compared mortality gradients in more- and less-equal states. Results. Mortality rates more strongly associated with county income were more strongly associated with state income inequality: across all mortality rates, r = −0.81; P =.004. The effect of state income inequality on the socioeconomic gradient in health varied by cause of death, but greater equality usually benefited both wealthier and poorer counties. Conclusions. Although mortality rates with steep socioeconomic gradients were more sensitive to income distribution than were rates with flatter gradients, narrower income differences benefit people in both wealthy and poor areas and may, paradoxically, do little to reduce health disparities. The nature of the association between income distribution and population health is of crucial importance to public health. The United States has wider income differences and a lower life expectancy than other developed countries, which appears to fit the international correlation between the 2. 1 Likewise, life expectancy among the 50 states also appears to be correlated with state income distribution. 2 However, despite a growing body of research and supportive findings from a large majority of published papers, disagreement remains about whether income inequality is a determinant of population health, 3 , 4 the nature of the processes through which it might influence population health, and how those processes might be related to the causes of health inequalities. A deeper understanding of these issues may pave the way for policymakers to improve population health and reduce health inequalities. An initially plausible hypothesis is that both the socioeconomic gradient in health and the association between health and income distribution reflect the effects of socioeconomic disadvantage on health; if narrower income differences reduce disadvantage, they might improve average health by reducing health disparities. However, it is also possible that any effects of income distribution could reflect quite separate causal processes from those responsible for the socioeconomic gradient in health. Although health disparities are sometimes attributed primarily to material and behavioral factors such as smoking, diet, bad housing, and lack of health care, 5 – 7 we and others have suggested that income inequality is more likely to influence health through processes of social comparison. 8 – 10 It is even possible that there are 2 completely separate domains: health inequalities may reflect the direct effects of material living standards, and income inequality may reflect the psychosocially mediated effects of social comparisons. Determining whether income inequalities work through the same or different processes from those responsible for health disparities is complicated by our lack of precise knowledge of the causal processes for either. Therefore, it would be informative to examine whether mortality rates that have steep socioeconomic gradients are also those most strongly related to income inequality and whether mortality rates that have little or no socioeconomic gradient have little or no relation to income inequality. Are mortality rates that are sensitive to the causes of health disparities also sensitive to income inequality?
