A strong and consistent finding of epidemiologic research is that there are health differences among socioeconomic groups. Lower mortality, morbidity, and disability rates among socioeconomically advantaged people have been observed for hundreds of years and have been replicated using various indicators of socioeconomic status (SES) and multiple disease outcomes (Kaplan and Keil, 1993; Syme and Berkman, 1976). Educational differentials in mortality have increased over the past three decades in this country (Feldman et al., 1989; Pappas et al., 1993; Tyroler et al., 1993). Moreover, formal comparisons of the mortality differences associated with education show that relationships between educational attainment and mortality are stronger in the United States than they are in most European countries (Kunst and Mackenbach, 1994).
Results from the National Longitudinal Mortality Study (NLMS) are representative of recent research that has documented the link between SES and health. The NLMS is a large national database on the U.S. noninstitutionalized population assembled from survey information collected between 1978 and 1985; deaths were ascertained using the National Death Index for 1979–1989 (Sorlie et al., 1995). Mortality was strongly associated with education, income, and occupation (Rogot et al., 1992; Sorlie et al., 1992, 1995). For example, among those aged 25–64, white men and women with 0–4 total years of education had age-adjusted death rates that were 66% and 44% higher, respectively, than those with 5 or more years of college. For African American men and women, the corresponding increases in mortality were 73% and 78%, respectively. Similar findings were observed when income was used as a proxy for SES. Age-adjusted death rates among white men and women with annual family incomes of less than $5,000 were 80% and 30% higher, respectively, than were those among their counterparts in households with incomes of $50,000 or more. As with education, even greater differentials were seen among African Americans: men in African American households earning less than $5,000 were twice as likely to die during follow-up than were those in families earning $50,000 or more. Poor African American women were 80% more likely to die than were wealthier women.
Socioeconomic differentials in mortality have been observed for many causes of death. The Multiple Risk Factor Intervention Trial (MRFIT) followed 320,909 white and African American men for 16 years (Davey Smith et al., 1996a,b). Median family income in ZIP code of residence was predictive of death from a variety of medical conditions in analyses