Modelling health,income and income inequality: the impact of income inequality on health and health inequality

A framework is developed to analyse the impact of the distribution of income on individual health and health inequality, with individual health modelled as a function of income and the distribution of income. It is demonstrated that the impact of income inequality can generate non-concave health production functions resulting in a non-concave health production possibility frontier. In this context, the impact of different health policies are considered and it is argued that if the distribution of income affects individual health, any policy aimed at equalising health, which does not account for income inequality, will lead to unequal distributions of health. This is an important development given current UK government attention to reducing health inequality.     

Neighbourhood inequality, neighbourhood affluence and population health

While there is now considerable evidence that the neighbourhood income levels (poverty/affluence) exert an independent effect on health, there is little evidence that neighbourhood income inequality is consequential, net of individual-level socio-economic resources. We show that the usual explanation for the absence of an independent effect of neighbourhood inequality--the assumption of economic homogeneity at the neighbourhood level--cannot account for this result. The authors use hierarchical models that combine individual micro-data from Statistics Canada's 1996/97 National Population Health Survey (NPHS) with neighbourhood and city-level socio-economic characteristics from the 1996 Census of Canada to estimate the effects of neighbourhood affluence and income inequality on self-reported health status. The findings indicate that the negative "ecological" correlation between average neighbourhood health and neighbourhood income inequality is the result not only of compositional differences among individuals but also of contextual neighbourhood effects associated with low and high inequality neighbourhoods.     

Peripherality, income inequality, and life expectancy: revisiting the income inequality hypothesis

BACKGROUND: Recent criticisms of the income inequality and health hypothesis have stressed the lack of consistent significant evidence for the stronger effects of income inequality among rich countries. Despite such criticisms, little attention has been devoted to the income-based criteria underlying the stratification of countries into rich/poor groups and whether trade patterns and world-system role provide an alternative means of stratifying groups. METHODS: To compare income-based and trade-based criteria, 107 countries were grouped into four typologies: (I) high/low income, (II) OECD membership/non-membership, (III) core/non-core, and (IV) non-periphery/periphery. Each typology was tested separately for significant differences in the effects of income inequality between groups. Separate group comparison tests and regression analyses were conducted for each typology using Rodgers (1979) specification of income, income inequality, and life expectancy. Interaction terms were introduced into Rodgers specification to test whether group classification moderated the effects of income inequality on health. RESULTS: Results show that the effects of income inequality are stronger in the periphery than non-periphery (IV) (-0.76 vs -0.23; P < 0.05). An incremental F-test confirmed significant differences in the coefficient subsets between the two groups (F(2,101) = 6.31; P < 0.01). CONCLUSIONS: Cross-national analyses of income inequality and population health have assumed (i) income differences between countries best capture global stratification and (ii) the negative effects of income inequality are stronger in high-income countries. However, present findings emphasize (i) the importance of measuring global stratification according to trading patterns and (ii) the strong, negative effects of income inequality on life expectancy among peripheral populations.     

The impact of income inequality on individual and societal health: absolute income, relative income and statistical artefacts

The relative income hypothesis, that relative income has a direct effect on individual health, has become an important part of the literature on health inequalities. This paper presents a four-quadrant diagram, which shows the effect of income, relative income and aggregation bias on individual and societal health. The model predicts that increased income inequality reduces average health regardless of whether relative income affects individual health. If relative income does have a direct effect then societal health will decrease further.     

Beyond the income inequality hypothesis: class, neo-liberalism, and health inequalities

This paper describes and critiques the income inequality approach to health inequalities. It then presents an alternative class-based model through a focus on the causes and not only the consequences of income inequalities. In this model, the relationship between income inequality and health appears as a special case within a broader causal chain. It is argued that global and national socio-political-economic trends have increased the power of business classes and lowered that of working classes. The neo-liberal policies accompanying these trends led to increased income inequality but also poverty and unequal access to many other health-relevant resources. But international pressures towards neo-liberal doctrines and policies are differentially resisted by various nations because of historically embedded variation in class and institutional structures. Data presented indicates that neo-liberalism is associated with greater poverty and income inequalities, and greater health inequalities within nations. Furthermore, countries with Social Democratic forms of welfare regimes (i.e., those that are less neo-liberal) have better health than do those that are more neo-liberal. The paper concludes with discussion of what further steps are needed to "go beyond" the income inequality hypothesis towards consideration of a broader set of the social determinants of health.     

Social capital, income inequality, and self-rated health in 45 countries

There has been growing interest in the relationship between the social environment and health. Among the concepts that have emerged over the past decade to examine this relationship are socio-economic inequality and social capital. Using data from the World Values Survey and the World Bank, we tested the hypothesis that self-rated health is affected by social capital and income inequality cross-nationally. The merit of our approach was that we used multilevel methods in a larger and more diverse sample of countries than used previously. Our results indicated that, for a large number of diverse countries, commonly used measures of social capital and income inequality had strong compositional effects on self-rated health, but inconsistent contextual effects, depending on the countries included. Cross-level interactions suggested that contextual measures can moderate the effect of compositional measures on self-rated health. Sensitivity tests indicated that effects varied in different subsets of countries. Future research should examine country-specific characteristics, such as differences in cultural values or norms, which may influence the relationships between social capital, income inequality, and health.     

Changes in income inequality and the health of immigrants

Research suggests that income inequality is inversely associated with health. This association has been documented in studies that utilize variation in income inequality across countries or across time from a single country. The primary criticism of these approaches is their inability to account for potential confounders that are associated with income inequality. This paper uses variation in individual experiences of income inequality among immigrants within the United States (U.S.) to evaluate whether individuals who moved from countries with greater income inequality than the U.S. have better health than those who migrated from countries with less income in equality than the U.S. Utilizing individual-level (March Current Population Survey) and country-level data (the United Nations Human Development Reports), we show that among immigrants who have resided in the U.S. between 6 and 20 years, self-reported health is more favorable for the immigrants in the former category (i.e., greater income inequality) than those in the latter (i.e., lower income inequality). Results also show that self-reported health is better among immigrants from more developed countries and those who have more years of education, are male, and are married.     

Poverty, wealth inequality and health among older adults in rural Cambodia

Little research exists on health determinants among adults living in economically deprived regions despite the fact that these areas comprise a good part of the world. This paper examines the distribution of wealth then tests associations between wealth inequality and a variety of health outcomes, among older adults, in one of the world's poorest regions--rural Cambodia. Data from the 2004 Survey of the Elderly in Cambodia are employed. Using a disablement framework to conceptualize health, associations between four health components and a wealth inequality measure are tested. The wealth inequality measure is based on an index that operationalizes wealth as ownership of household assets and household structural components. Results confirm difficult economic conditions in rural Cambodia. The lowest wealth quintile lives in households that own nothing, while the next quintiles are only slightly better off. Nevertheless, logistic regressions that adjust for other covariates indicate heterogeneity in health across quintiles that appear qualitatively similar, with the bottom quintiles reporting the most health problems. An exception is disability, which presents a U-shaped association. It is difficult to determine mechanisms behind the relationship using cross-sectional data, but the paper speculates on possible causal directions, both from wealth to health and vice-versa. The analysis suggests the ability to generalize the relationship between wealth inequality and health to extremely poor populations as a very small difference in wealth makes a relatively large difference with respect to health associations among those in meager surroundings.     

Social capital and health (plus wealth, income inequality and regional health governance)

This article describes an empirical exploration of relationships among aspects of thirty health districts in Saskatchewan, Canada. These aspects include social capital, income inequality, wealth, governance by regional health authorities and population health, the primary dependent variable. The social capital index incorporated associational and civic participation, average and median household incomes served as proxies for wealth, the degree of skew in the distribution of household incomes assessed income inequality while the model for effective governance by District Health Boards (DHBs) focused on reflection of health needs, policy making and implementation, fiscal responsibility and the integration and co-ordination of services. I found no evidence of a relationship between social capital in health districts and the performance of DHBs. Among the determinants of health, wealth appeared unrelated to age-standardised mortality rates while income inequality was positively and social capital was negatively related to mortality. Income inequality was not as strongly related to age-standardised mortality after controlling for social capital. and vice versa, suggesting the two may be comingled somehow when it comes to population health, although they were not significantly related to one another. Of the predictors of social capital the distribution of age in districts appeared to be the most salient; of the predictors of age-standardised mortality rates the gender composition of a district was most salient.     

Income inequality,household income,and health status in Canada: a prospective cohort study

OBJECTIVES: This study sought to determine whether income inequality, household income, and their interaction are associated with health status. METHODS: Income inequality and area income measures were linked to data on household income and individual characteristics from the 1994 Canadian National Population Health Survey and to data on self-reported health status from the 1994, 1996, and 1998 survey waves. RESULTS: Income inequality was not associated with health status. Low household income was consistently associated with poor health. The combination of low household income and residence in a metropolitan area with less income inequality was associated with poorer health status than was residence in an area with more income inequality. CONCLUSIONS: Household income, but not income inequality, appears to explain some of the differences in health status among Canadians.     

Population health and income inequality: new evidence from Israeli time-series analysis

BACKGROUND AND OBJECTIVES: The relationship between population health and inequality in income distribution has attracted much attention during the last two decades. The purpose of this paper is to examine that relationship using Israeli time-series data, and considering three types of income: economic, pre-tax, and disposable. METHODS: Israeli time series (1979-2000) on life expectancy of men and women at birth and at ages 5 and 65, as well as infant mortality, were related to Gini coefficients measuring inequality in economic, pre-tax (after transfers) and disposable (after taxes) incomes, controlling for gross domestic product (GDP) per capita. This design allows for the estimation of the effects on population health of changes in income inequalities over time as well as of contemporaneous reduction in inequality due to transfers and taxes. RESULTS: None of the three income inequality measures by itself had an effect over time on population health. However, larger contemporaneous reductions in inequality, mainly through the transfers system, were associated with better population health, in particular with lower infant mortality. CONCLUSIONS: A significant part of the temporal improvement in the health of the Israeli population has been due to the increasing effort to reduce inequality in economic income by increasing transfer payments. The results are generally inconsistent with the argument of adverse psychosocial effects of inequality on health, and are consistent with inequality being related to other harmful public goods affecting health and with Rodgers' argument.     

An exploratory multilevel analysis of income,income inequality and self-rated health of the elderly in China

In the last three decades, China has experienced rapid economic development and growing economic inequality, such that economic disparities between rural and urban areas, as well as coastal and interior areas have deepened. Since the late 1990s China has also experienced an ageing population which has attracted attention to the wellbeing of the rapidly growing number of elderly. This research aims to characterise province differences in health and to explore the effects of individual income and economic disparity in the form of income inequality on health outcomes of the elderly. The study is based on the Chinese Longitudinal Healthy Longevity Survey data collected in 2008 for 23 provinces. Multilevel logistic models are employed to investigate the relationship between income, income inequality and self-rated health for the elderly using both individual and province-level variables. Results are presented as relative odds ratios, and for province differentials as Median Odds Ratios. The analysis is deliberately exploratory so as to find evidence of income effects if they exist and particular attention is placed on how province-level inequality (contemporaneous and lagged) may moderate individual relationships. The results show that the health of the elderly is not only affected by individual income (the odds of poor health are 3 times greater for the elderly with the lowest income compared to those at the upper quartile) but also by a small main effect for province-level income inequality (odds ratio of 1.019). There are significant cross-level interactions such that where inequality is high there are greater differences between those with and without formal education, and between men and women with the latter experiencing poorer health.     

An examination of the relationship between neighborhood income inequality, social resources, and obesity in Los Angeles county

PURPOSE. This study examines whether local income inequality is associated with an increased likelihood of obesity among Los Angeles County residents and whether collective efficacy mediates the relationship. DESIGN. A cross-sectional study of 2875 adults in 65 neighborhoods that took part in wave 1 of the Los Angeles Family and Neighborhood Survey in 2000-2001. Neighborhood measures are taken from the Los Angeles Neighborhood Services and Characteristics Database and decennial census. MEASURES. Obesity is defined as a body mass index over 30. Income inequality is operationalized with the Gini coefficient. Collective efficacy is a neighborhood-level measure comprised of aggregated responses to items that capture trust, cohesion, and the willingness to intervene for the common good among residents. Controls are included at the individual level for demographics and health characteristics, and at the neighborhood level for median household income. ANALYSIS. Logistic regression models of individuals within neighborhoods. RESULTS. When neighborhood economic well-being is controlled, income inequality is associated with a significant reduction in the likelihood of obesity while also controlling for individual demographic and health-related characteristics. Collective efficacy exerts an independent and beneficial effect but does not mediate the relationship between inequality and obesity. CONCLUSION. Neighborhood social resources and economic heterogeneity are associated with a lower likelihood of obesity. It may be that economically heterogeneous neighborhoods, perhaps especially in Los Angeles County, contain characteristics that promote health.     

Measuring income related inequality in health: standardisation and the partial concentration index

The partial concentration index (PCI) is commonly used as a measure of income related inequality in health after removing the effects of standardising variables such as age and gender which affect health, are correlated with income, but not amenable to policy. Both direct and indirect standardisation have been used to remove the effects of standardising variables. The paper shows that with individual level data direct standardisation is possible using the coefficients from a linear regression of health on income and the standardising variables and yields a consistent estimate of the PCI. Indirect standardisation estimates the effects of the standardising variables on health from a health regression which excludes income. The coefficients on the standardising variables include some of the effects of income on health if income is correlated with the standardising variables. Using these coefficients to remove the effects of the standardising variables also removes some of the effect of income on health and leads to an inconsistent estimate of the PCI. Indirect standardisation underestimates the PCI irrespective of the signs of the correlations of standardising variables and income with each other and with health. An adaptation of the PCI when the marginal effect of income on health depends on the standardising variables is also proposed.     

Different income information as an indicator for health inequality among Japanese adults

BACKGROUND: There are several alternative indicators of income information, which is a fundamental measure of individual socioeconomic position. In this study, we compared the degrees of associations of four types of income information with health variables among Japanese adults. METHODS: Using a nationally representative sample of 29,446 men and 32,917 women aged 20 years and over, the associations between four income indicators and health variables were examined using the odds ratio in logistic regression analysis and the concentration index by sex and age group (20-59 years and 60+ years). Income indicators consisted of total household income, equivalent household income, total household expenditure, and equivalent household expenditure. Current smoking and self-rated health statuses were used as health variables. RESULTS: A low income was associated with a high prevalence of smoking and fair/poor self-rated health, with some differences among sex and age groups and income indicators, but less difference among methods of statistical analyses. Total and equivalent incomes were similarly and more markedly associated with smoking and self-rated health statuses, whereas equivalent expenditure showed the smallest degree of health difference. For the population aged 60+ years, the degree of health differences in smoking was similar between income and expenditure. CONCLUSIONS: Although the degree of income-related health differences is dependent on health outcome and both sex and age group, this study suggests that either crude or equivalent household income is a useful indicator for health inequality among Japanese adults.