A comparison of the relationships of education and income with mortality: the national longitudinal mortality study

A sample of over 400.000 men and women, ages 25-64, from the National Longi tudinal Mortality Study (NLMS), a cohort study representative of the nonins titutionalized US population, was followed for mortality between the years of 1979 and 1989 in order to compare and contrast the functional forms of t he relationships of education and income with mortality. Results from the s tudy suggest that functional forms for both variables are nonlinear. Educat ion is described significantly better by a trichotomy (represented by less than a high school diplomat a high school diploma or greater but no college diploma, or a college diploma or greater) than by a simple linear function for both men (p < 0.0001 for lack of fit) and women (p = 0.006 for lack of fit). For describing the association between income and mortality, a two-s loped function, where the decrease in mortality associated with a US$1000 i ncrease in income is much greater at incomes below US$22,500 than at income s above US$22,500, fits significantly better than a linear function for bot h men (p < 0.0001 for lack of fit) and women (p = 0.0005 for lack of fit). The different shapes for the two functional forms imply that differences in mortality may primarily be a function of income at the low end of the soci oeconomic continuum, but primarily a function of education at the high end. Published by Elsevier Science Ltd.