Explaining cross-national disparities in health: The role of income inequality

Previous studies report a strong negative association between income inequality and population health at the aggregate level. However whether this ecological association indicates a genuine, causal effect of income inequality on health, or it simply reflects a nonlinear effect of individual income on health, is still in hot debate in studies of public health and social epidemiology.;This dissertation aims to draw on empirical data to examine the association between income inequality and population health and test these alternative hypotheses. Specifically, I first examine whether the ecological association between income inequality and population health indicators is robust. I proposed a strategy to enhance the cross-national comparability of income inequality estimates available in second-hand data. Using the adjusted income inequality measures, there is a strong negative correlation between income inequality and life expectancy among 130 countries in the world. Controlling for GDP per capita, public health expenditure per capita and many other country characteristics does not eliminate the association between income inequality and life expectancy. Subsequently, I analyze the relationship between individual income, income inequality, and self-rated general health in a multilevel framework for 53 countries. Results show no independent association between country income inequality and individual self-rated general health. In contrast, self-rated general health is strongly associated with absolute material conditions both at the individual and at the country level. Hence the ecological association between income inequality and population health is more likely a reflection of the nonlinear effect of individual income on health rather than an independent effect of income inequality. Finally, I use social surveys in three developing countries to examine the validity of self-rated general health. Results demonstrate that self-rated general health is a very comprehensive indicator of individual perceived health, but is only weakly associated with other objective health measures for all three countries. Moreover, there is evidence that self-rated general health is contaminated by heterogeneous reporting styles among social groups. The pattern of reporting heterogeneity is complex and differs from one country to another. Consequently, it is recommended to collect and examine other objective health indicators together with self-rated general health in social surveys.