A new measure of lifetime disparity

Numerous studies show that high life expectancy is closely related to low life disparity. Unlike life expectancy, which can be increased by mortality decline at any age, averting deaths may either reduce or increase life disparity. Disparity can thus be decomposed into two opposite components, called compression and expansion, according to the effect of mortality decline on the age distribution of mortality. Conventional measures of disparity do not distinguish between the two components and inevitably provide misleading information on the equalization of life chances in a population. Based on the relevant properties of the change in disparity, we develop a new measure of disparity, the ratio of expansion to compression (REC), which can account for the relative importance of the two components. With this simple measure, we can obtain not only a clearer vision of the evolution of disparity, but also a consistent interpretation of the change in disparity related to mortality decline, just as we do with life expectancy. Empirical analysis shows the advantages of the new measure over conventional measures of disparity.