Age structure, the life course and "aged heterogeneity": prospects for research and theory.

A widespread generalization in the study of aging is that old people are the most heterogeneous of any age group on a wide variety of characteristics. This phenomenon has several implications for thinking about aging. First, if cohorts or age strata vary systematically in their distributions on a given characteristic, then the dominant practice of comparing them primarily on measures of central tendency may obscure significant aspects of aging. Second, attention to systematic differences in variability points to the need to distinguish life-course, cohort and period dynamics in the production of patterns of variability. From a life-course perspective the construction of intracohort trajectories of variability for successive cohorts can disentangle these potentially confounded processes. Examining intracohort variability as outcome, we consider several hypothetical trajectories of variability, describe the kinds of processes likely to underlie each, and suggest hypothetical examples of characteristics to which each may apply. Finally, we consider the possible influence of age strata differences in intrastratum variability upon other aspects of social structure and upon individual aging.