Objectives: This study examined whether state income inequality was associated with an individual's limitations in activities of daily living (ADL) when controlling for the individual's demographic and socio-economic characteristics.
Study design and methods: The study was based on secondary analyses of data collected in the 2003 American Community Survey (ACS). The ACS is a national survey of Americans with a 96.7% response rate. The sample used for this research included 645,835 participants aged 25 years and older. A multilevel model with a non-linear logit link function was used.
Results: A 0.05 increase in the Gini coefficient (a measure of state level income inequality) was associated with an increase of 11% in the odds of ADL limitations [odds ratio (OR) 1.11, 95% confidence intervals 1.01-1.22] even after controlling for the individual's demographic and socio-economic characteristics. These elevated odds are comparable with those associated with women in comparison with men (OR 1.12). A separate analysis indicated that individuals in the three least equitable states had consistently higher probabilities of ADL limitations across the whole economic spectrum when compared with individuals in the three most equitable states.
Conclusions: State-level income inequality and individual income levels were significant independent predictors of ADL limitations. The impact of any future changes in state-level income inequality or shifts in individual income levels in the USA could be used to further investigate if this relationship is causal.