The long-term impact of income inequality on health has not been fully explored in the current literature. Until now, 4 studies have examined the lagged effect on population/group mortality rate at the aggregate level, and 7 studies have investigated the effect of income inequality on subsequent individual mortality risk within a restricted time period. These 11 studies suffer from the same limitation: they do not simultaneously control for a series of preceding income inequalities. The results of these studies are also mixed. Using the U.S. National Health Interview Survey data 1986-2004 with mortality follow-up data 1986-2006 (n = 701,179), this study investigates the lagged effects of national-level income inequality on individual mortality risk. These effects are tested by using a discrete-time hazard model where contemporaneous and preceding income inequalities are treated as time-varying person-specific covariates, which then track a series of income inequalities that a respondent faces from the survey year until s/he dies or is censored. Findings suggest that income inequality did not have an instantaneous detrimental effect on individual mortality risk, but began exerting its influence 5 years later. This effect peaked at 7 years, and then diminished after 12 years. This pattern generally held for three measures of income inequality: the Gini coefficient, the Atkinson index, and the Theil entropy index. The findings suggest that income inequality has a long-term detrimental impact on individual mortality risk. This study also explains discrepancies in the existant literature.
Copyright © 2012 Elsevier Ltd. All rights reserved.