Education and the changing shape of the income gradient in health

Research on the social determinants of health has increasingly sought to understand the relative importance of different features of socioeconomic status. Much of the ensuing debate has wavered between education and income, with recent research leaning increasingly toward income. This research has not, however, consistently explored interactions between different features of socioeconomic status and, in trying to understand the independent effects of different components of socioeconomic status, may have missed important features of socioeconomic position. With an eye toward examining how features of socioeconomic status combine and coalesce, this paper examines variation in the income-health association by level of education. Theories derived both from medical sociology and health economics suggest synergistic interactions between income and education, but they are unclear as to the direction and magnitude of these interactions. Results from two large and nationally representative data sets (the 1996-1997 Community Tracking Study and the 1972-2000 General Social Survey) indicate that the positive relationship between income and health varies substantially in both its strength and shape by level of education. Education improves health, and its effects are larger at lower levels of income. Moreover, education reduces the strength and curvature of the income-health relationship. Consequently, those with more education have better health for all levels of income, and fewer income-based disparities exist among the well educated than among the less well educated. The linear "gradient" relationship between income and health is, thus, more characteristic of groups with higher levels of education. Additional analyses indicate that these interactions existed in the United States in each of the last three decades. The results are discussed in light of theory regarding the perpetuation of health disparities, as well as current debates regarding the apparent incompatibility of distributive versus aggregative goals in health policy.