How Inequality Affects Health: Reconciling Evidence from Cross-Sectional, Relational, and Longitudinal Analyses

The income inequality hypothesis is one of the most influential ideas in public health. It posits that in the affluent world income inequality per se has a direct, independent and detrimental effect on health. This hypothesis, established in the 1990s, led to the publication of hundreds of articles across multiple disciplines. This hypothesis is also rather controversial. Debates surround the actual effect of income inequality and the hypothesized mechanisms. The evidence is consistently inconsistent. I argue that several conceptual and methodological limitations afflict this literature and hinder our understanding of the relationship between income inequality and health. In particular, I highlight four limitations: 1) simplistic treatment of inequality and poverty; 2) reliance on cross-national ecological comparisons that do not adequately consider the contributions of unusual cases; 3) reliance on cross-sectional comparisons; 4) reliance on a limited use of indicators. These limitations prompted the present dissertation research, which comprises three empirical studies. In the first study, I reanalyze publicly available data on income inequality and health across 20 affluent countries and 50 U.S. states. Drawing on the analytical difference between gap and headcount measures of income distributions, I argue that income inequality and poverty are dependent but distinct, and I estimate the extent to which poverty rates modify the relationship between income inequality and health. Across countries, the interaction of income inequality and poverty has a significant and adverse effect on health. Across U.S. states, instead, the interaction is not significant because the effect of poverty completely nullifies the effect of income inequality. In the second study, I delve into the interaction observed when comparing affluent countries in the first study. I use a recently developed methodology that decomposes regression coefficient estimates into unique case-specific contributions. I focus on the most frequently used measure of population health, life expectancy. I estimate OLS regression models with four different model specifications, which I then decompose. Four cases make major contributions to the coefficient estimates in all of the models. Two of these cases, Denmark and Japan, are particularly important because they challenge theoretical expectations: Denmark shows remarkably low life expectancy despite low levels of income inequality and poverty; Japan has the highest life expectancy despite relatively high levels of poverty. Denmark’s low life expectancy is explained by the high mortality risk of women born between WWI and WWII, who exhibited a lifelong high propensity to smoke. Japan’s high life expectancy is due to a concerted series of government initiatives (e.g., establishment of universal health insurance coverage, salt reduction campaigns, cost-effective antihypertensive drugs, dietary guidelines) that promoted healthy lifestyles and dietary habits. In the third and final study, I examine the income inequality hypothesis longitudinally. I estimate the effect of three indicators of income inequality (Gini coefficient, top 0.1% income share, and Theil index) on four outcomes (death rates for suicide, drug poisoning, homicide and heart disease) across the 50 U.S. states in 2000-2015. I estimate fixed-effects models that account for unobserved heterogeneity and omitted variable bias. My findings show no effect of income inequality on health. Lastly, I estimate mediation models that assess the indirect effect of income inequality on health via welfare generosity (in particular, the SNAP program, formerly known as the Food Stamp Program.) Across all specifications, income inequality has a negative indirect effect on mortality. Income inequality increases welfare generosity, which improves population health. As a whole, this dissertation shows that in the affluent world, income inequality has no direct or independent effect on health. Supporting individuals and household with no or low income might be a better way to improve population health than just reducing income inequality

Recalibrating the spirit level: An analysis of the interaction of income inequality and poverty and its effect on health

The publication of The Spirit Level (Wilkinson & Pickett, 2009) marked a paramount moment in the analysis of health and inequality, quickly attracting a remarkable degree of attention, both positive and negative, both in academic and in public discourse. Following at least 20 years of research, the book proposes a simple and powerful argument: inequality per se, more specifically income inequality, is harmful to every aspect of social life. In order to confirm this idea, the authors present a series of bivariate, cross-sectional associations showing comparisons across countries and within the United States. Despite the methodological limitations of this approach, the authors advance causal claims concerning the detrimental effects of income inequality. They also rule out poverty as a plausible alternative explanation, without directly measuring it. Meanwhile, over the last decade stratification scholars have demonstrated the nonlinear effect of economic factors, especially income, on health. The results suggest that a relative approach is best for analyzing dynamics at the top of the income distribution, whereas an absolute approach seems most appropriate for studying the bottom of the distribution. Consistent with this perspective, here I reanalyze data from The Spirit Level, adding a measure of poverty, in order to control the effect of inequality and explore its interaction with poverty. The findings show that inequality and poverty—which I contend are two interdependent but nonetheless distinct phenomena—interact across countries, such that the detrimental effects of inequality are present or stronger in countries with high poverty, and absent or weaker in countries with low poverty; poverty replaces inequality as the favored explanation of health and social ills across states. The new evidence suggests that income distributions are characterized by a complex interplay between inequality and poverty, whose interaction deserves further analysis

Income Inequality and Chronic Health Conditions: A Multilevel Analysis of the U.S. States

Recently, much scholarly work has been conducted examining the effect of rising income inequality on health outcomes. However, this work is somewhat inconclusive. Chiefly, the mechanisms which could produce such an association are still being sorted out. Further, much of this work is focused on mortality outcomes with little attention to how this process operates for actual health conditions, including chronic health problems, which are arguably now the main public health concerns of the developed world. In this study, in a series of multilevel binary logistic regression models using data from the 2005 and 2007 Behavioral Risk Factor Surveillance System (BRFSS), we examine the association between state-level income inequality, poverty, and social welfare measures on spending and policy to examine the association between these factors for three chronic health outcomes: diabetes, hypertension, and coronary heart disease. We find that income inequality is only conditionally positively related to the diagnosis of two of the three outcomes, diabetes and hypertension, and only in 2007. However, absolute poverty is related to the outcome across all three dependent variables. Additionally, certain social welfare measures attenuate the effects of both income inequality and absolute poverty, suggesting that certain welfare policies reduce this association

Sad Eyes, Crooked Crosses: Religious Struggles, Psychological Distress and the Mediating Role of Psychosocial Resources

In this paper, we employed data from the 2011 Miami-Dade Health Survey (n = 444) to formally test whether the association between religious struggles and psychological distress is mediated by psychosocial resources. We found that religious struggles were associated with lower levels of social support, self-esteem, the sense of control, and self-control. We also observed that religious struggles were associated with higher levels of non-specific emotional distress, depression, and anxiety, but not somatization. Our mediation analyses revealed significant indirect effects of religious struggles on emotional distress (not somatization) through social support, self-esteem, and the sense of control, but not self-control