Kennedy BP, Kawachi I, Prothrow-Stith D. Income distribution and mortality: cross sectional ecological study of the Robin Hood index in the United States. British Medical Journal 1996; 312: 1004-7.

This important study, published simultaneously with the Kaplan paper above, demonstrated the income inequality health relationship carried out on similar US data, but using different measures for income distribution. The Robin Hood Index used, is the proportion of money needed to be transferred from the rich to the poor to achieve equality. The analysis complemented the Kaplan study by looking at not only all cause mortality, but disease specific mortality, and also corrected for different poverty measures, again showing that it is relative deprivation, rather than absolute poverty that matters. The relationship was observed when adjusted for household size, and was present for both white and black races. The effect of income distribution on black mortality was greater than white, after controlling for state levels of poverty. The association was found for infant mortality, and for coronary heart disease, as well as cancers, and homicide. When adjusting the data for differential prevalence of smoking, and poverty, the relationship was attenuated, but still present for all cause and disease specific mortality. The Robin Hood Index of income inequality was also associated with cause specific mortality from heart disease, infectious diseases, hypertension, tuberculosis and homicide findings that were independent of state poverty levels and prevalence of smoking. 

Abstract

OBJECTIVE--To determine the effect of income inequality as measured by the Robin Hood index and the Gini coefficient on all cause and cause specific mortality in the United States. 

DESIGN--Cross sectional ecological study. 

SETTING--Households in the United States. 

MAIN OUTCOME MEASURES--Disease specific mortality, income, household size, poverty, and smoking rates for each state. 

RESULTS--The Robin Hood index was positively correlated with total mortality adjusted for age (r = 0.54; P < 0.05). This association remained after adjustment for poverty (P < 0.007), where each percentage increase in the index was associated with' an increase in the total mortality of 21.68 deaths per 100,000. Effects of the index were also found for infant mortality (P = 0.013); coronary heart disease (P = 0.004); malignant neoplasms (P = 0.023); and homicide (P < 0.001). Strong associations were also found between the index and causes of death amenable to medical intervention. The Gini coefficient showed very little correlation with any of the causes of death. 

CONCLUSION--Variations between states in the inequality of income were associated with increased mortality from several causes. The size of the gap between the wealthy and less well off--as distinct from the absolute standard of living enjoyed by the poor--seems to matter in its own right. The findings suggest that policies that deal with the growing inequities in income distribution may have an important impact on the health of the population.

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Keywords

• Gini coefficient
• cause specific mortality
• confounding
• ecological studies
• education
• heart disease
• homicide
• income
• income distribution
• income inequality
• infant mortality
• medical care
• mortality
• population health
• race
• regional
• relative deprivation
• smoking
• social capital
• social stratification
• socioeconomic status
• unemployment
• wealth inequality