Analysis of life course processes requires longitudinal data and methodological strategies that can assess trajectories of change in social ties and health habits over long periods. A number of high-quality longitudinal data sets have produced much of the evidence reviewed here. For example, many of the outstanding studies on adolescent health habits rely on the Add Health data (e.g., Crosnoe 2006). Studies on adult health habits rely on several excellent data sets, including the Health and Retirement Survey (e.g., Hayward et al. 2000) and the Americans’ Changing Lives Survey (e.g., Umberson et al. 2008). Although the data on adult populations often include retrospective reports of childhood experiences, future population research that follows young people throughout the life course is likely to yield unique insights into the cascading and cumulative effects of social ties on health habits and, ultimately, on health outcomes throughout life. The growing availability of biomarker data attached to survey data at the population level (e.g., the National Social Life Health and Aging Project, Waite et al. 2008) provides new opportunities for assessing the interplay of physiological, psychological,
