County-level income inequality and depression among older Americans.

Researchers have consistently demonstrated a strong association between socioeconomic status (SES) and health at the individual level (Robert 1998; Smith 1998). What is new is an increasing interest in how socioeconomic conditions of the area of residence influence individuals' lives and health (House 2002; Robert 1998; 1999; Smith 1999). In particular, the relative income hypothesis (Wilkinson 1992; 1996) has stimulated a number of empirical and theoretical papers that attempt to support or question its tenet that the relative SES position, in addition to the absolute level of income, affects health. To refute or confirm the ecological studies that found associations between income inequality, or distribution of individual income, and population mortality across countries (Rodgers 1979; Wilkinson 1992; 1996) and within the United States (Kaplan et al. 1996; Kennedy, Kawachi, and Prothrow-Stith 1996; Lynch et al. 1998), researchers have attempted to test whether the degree of income inequality in the area of residence affects individuals' health independent of their income and demographic characteristics—the so called “income inequality hypothesis” (Wagstaff and van Doorslaer 2000). The majority of such studies were conducted using data on the United States (Blakely, Kennedy, and Kawachi 2001; Blakely, Lochner, and Kawachi 2002; Daly et al. 1998; Diez-Roux, Link, and Northridge 2000; Fiscella and Franks 1997; 2000; Kahn et al. 2000; Kennedy et al. 1998; Lochner et al. 2001; Soobader and LeClere 1999; Subramanian, Kawachi, and Kennedy 2001), and have provided limited support for the hypothesis. Further empirical studies as well as theoretical work is needed to make sense of inconsistent research findings and to figure out whether the strengths, nature, and underlying mechanisms of income inequality on health depend on dimensions of health, units of geographical aggregation (e.g., country, state, or community), and the population of focus. At this point, little is known about how income inequality in areas smaller than states is associated with mental health. Relative lack of attention to the psychological dimension of health is somewhat surprising, given that researchers often assume that income inequality exerts noxious psychological effects that lead to ill health (Kawachi and Kennedy 1999). Furthermore, older adults have been one of the least studied populations in this area even though older adults and children are considered to be more vulnerable to the environment where they live than younger adults (La Gory and Fitzpatrick 1992). To fill this gap of research, this article examines the association between county-level income inequality and depression among a nationally representative sample of Americans aged 70 and older, using the first wave of the Assets and Health Dynamics among the Oldest Old (AHEAD) survey linked with county-level decennial Census data of 1990. Depression is a superb indicator of older adults' well being (Mills and Henretta 2001; Mirowsky 1996). The main research questions are: Is county-level income inequality significantly associated with older adults' depression, controlling for county-level mean household income and individual-level demographic characteristics, SES (education, income and wealth), and physical health? And is the effect stronger among individuals with lower levels of SES and physical health?