THE RELATIONSHIP OF INCOME INEQUALITY TO MORTALITY - DOES THE CHOICE OF INDICATOR MATTER

Ecologic studies in the U.S. and elsewhere in the world have demonstra ted that income inequality is strongly related to mortality and life e xpectancy: the greater the dispersion of income within a given society , the lower the life expectancy. However, these empirical studies have been criticised on the grounds that the choice of indicator may have influenced positive findings. Using a cross-sectional, ecologic design , we tested the relationships of six different income inequality indic ators to total mortality rates in the 50 U.S. states. The following su mmary measures of income distribution were examined: the Gini coeffici ent; the decile ratio; the proportions of total income earned by the b ottom 50%, 60%, and 70% of households: the Robin Hood Index; the Atkin son Index; and Theil's entropy measure. All were highly correlated wit h each other (Pearson r greater than or equal to 0.94), and all were s trongly associated with mortality (Pearson r ranging from 0.50 to 0.66 ), even after adjustment for median income and poverty. Thus, the choi ce of income distribution measure does nor appear to alter the conclus ion that income inequality is linked to higher mortality. Furthermore, adjustment for taxes and transfers, as well as household size (using equivalence scales), made no difference to the income inequality/morta lity association. From a policy perspective, the alternative income di stribution measures perform differently under varying types of income transfers, so that theoretical considerations should guide the selecti on of an indicator to assess the impact of social and economic policie s that address income inequality. (C) 1997 Elsevier Science Ltd.