Objectives: This article overviews previously published and ongoing research from the Americans' Changing Lives (ACL) Study, a longitudinal study of a nationally representative sample of 3,617 adults aged 25 years and older when first interviewed in 1986, focusing on socioeconomic disparities in the way health changes with age during middle and later life, especially in terms of compression of morbidity/functional limitations.

Methods: A variety of descriptive and multivariate regression and growth curve analyses are done on the ACL sample, now surveyed over four waves spanning 15.5 years between 1986 and 2001/2002 with continuing mortality ascertainment via the National Death Index, death certificate searches, and informant reports.

Results: Both cross-sectional and longitudinal analyses indicate that socioeconomic disparities in health are small in early adulthood, increase through middle and early old age, and then lessen again in later old age. In other terms, compression of morbidity/functional limitations into the later stages of the life course is realized to a much greater degree among the better educated compared with the less educated. Cross-sectional evidence suggests that this reflects differential exposure to or experience of a wide range of psychosocial, environmental, and biomedical risk factors for health (and perhaps their differential impact at different ages and life stages), as well as variations in biological robustness and frailty and also perhaps in the strength of social welfare supports for health at different life stages. Longitudinal analyses reveal several new insights: (a) The flow of causality is much greater from socioeconomic position to health than vice versa; (b) education plays a greater role relative to income in the onset of functional limitations, whereas income has much stronger effects on their progression or course; and (c) educational disparities in the onset and hence of compression of functional limitations over the life course have increased strikingly in later middle and early old age (ages 55-84 years) since 1986.

Discussion: The results indicate that understanding and alleviating social disparities in health are both theoretically and methodologically quintessential problems of life course analysis and research.