Income Inequality and Population Health: Examining the Role of Social Policy

Causal Assessment of Income Inequality on Self-Rated Health and All-Cause Mortality: A Systematic Review and Meta-Analysis

Policy Points Income is thought to impact a broad range of health outcomes. However, whether income inequality (how unequal the distribution of income is in a population) has an additional impact on health is extensively debated. Studies that use multilevel data, which have recently increased in popularity, are necessary to separate the contextual effects of income inequality on health from the effects of individual income on health. Our systematic review found only small associations between income inequality and poor self-rated health and all-cause mortality. The available evidence does not suggest causality, although it remains methodologically flawed and limited, with very few studies using natural experimental approaches or examining income inequality at the national level.

CONTEXT

Whether income inequality has a direct effect on health or is only associated because of the effect of individual income has long been debated. We aimed to understand the association between income inequality and self-rated health (SRH) and all-cause mortality (mortality) and assess if these relationships are likely to be causal.

METHODS

We searched Medline, ISI Web of Science, Embase, and EconLit (PROSPERO: CRD42021252791) for studies considering income inequality and SRH or mortality using multilevel data and adjusting for individual-level socioeconomic position. We calculated pooled odds ratios (ORs) for poor SRH and relative risk ratios (RRs) for mortality from random-effects meta-analyses. We critically appraised included studies using the Risk of Bias in Nonrandomized Studies - of Interventions tool. We assessed certainty of evidence using the Grading of Recommendations Assessment, Development and Evaluation framework and causality using Bradford Hill (BH) viewpoints.

FINDINGS

The primary meta-analyses included 2,916,576 participants in 38 cross-sectional studies assessing SRH and 10,727,470 participants in 14 cohort studies of mortality. Per 0.05-unit increase in the Gini coefficient, a measure of income inequality, the ORs and RRs (95% confidence intervals) for SRH and mortality were 1.06 (1.03-1.08) and 1.02 (1.00-1.04), respectively. A total of 63.2% of SRH and 50.0% of mortality studies were at serious risk of bias (RoB), resulting in very low and low certainty ratings, respectively. For SRH and mortality, we did not identify relevant evidence to assess the specificity or, for SRH only, the experiment BH viewpoints; evidence for strength of association and dose-response gradient was inconclusive because of the high RoB; we found evidence in support of temporality and plausibility.

CONCLUSIONS

Increased income inequality is only marginally associated with SRH and mortality, but the current evidence base is too methodologically limited to support a causal relationship. To address the gaps we identified, future research should focus on income inequality measured at the national level and addressing confounding with natural experiment approaches.

The effect of environmental degradation on self-reported health: the role of renewable energy consumption

Although there are a number of studies in the literature that have explored the effect of environmental degradation on the subjective well-being and life satisfaction, no previous study has addressed the role of renewable energy consumption in examining the effect of environmental degradation on self-reported health. To this end, we employ a conditional mixed process (CMP) model, using a unique dataset that combines both micro-level data from the 6th (2010-2014) and 7th (2017-2022) Waves of the World Values Survey (WVS) database and macro-level data from the World Bank. Our study has several important empirical findings. First, while environmental degradation deteriorates self-reported health, social capital and health expenditure have a positive impact on self-reported health. Second, the share of renewable energy consumption in total final energy consumption has a statistically significant negative impact on environmental degradation. Third, urbanization has a deteriorating effect on environmental quality and the total number of people increases environmental degradation.

Income Support Policy Packages and Birth Outcomes in U.S. States: An Ecological Analysis

Research suggests that generous social welfare programs play a role in maternal and child health. However, most studies examine a single policy in isolation. Drawing from research documenting low-income families 'packaging' of social policies, we create a novel measure summarizing the value of a collection of income support policies for the working poor. This collection includes: the Supplemental Nutrition Assistance Program (SNAP), the Earned Income Tax Credit (EITC), the minimum wage, and the unemployment insurance (UI) program. Using U.S. state-level administrative data from 1996 to 2014, we estimate fixed effects regression models to examine the relationship between birth outcomes and income support policies (individually and combined). We find that increases in the combined value of the four income supports are significantly associated with reductions in preterm births and low birthweight births, but not infant mortality rates. States with the highest observed levels of combined income support had 14% fewer PTBs and 7% fewer LBWs than states with the lowest levels of income support. Of the four individual income support policies, only unemployment insurance has no significant independent effects. SNAP benefits have the largest and most consistent effects, reducing poor birth outcomes across all three indicators. An annual increase of $1000 in SNAP benefits is associated with a 3% decline in infant deaths, 5% decline in preterm births, and 2% decline in low birthweight births. These results suggest that increasing the generosity of income support policies may be a promising strategy for improving birth outcomes in the United States.