Gradual Change or Punctuated Equilibrium? Reconsidering Patterns of Health in Later-Life
Michal Engelman and Heide Jackson
This paper examines the curious mismatch between the supposition of gradual, continuous change embedded in common health trajectory models and a pattern of punctuated stability that is captured in the nationally-representative and widely-used Health and Retirement Study. Inspired by an insight from evolutionary biology, our analysis contrasts the conclusions drawn from mixed regression methods (growth curve models and latent class growth analysis) designed to capture trajectories in repeated-measure data with methods (multistate life tables and sequence analysis) designed to describe discrete states and transition patterns. Although a gradually increasing number of functional limitations is consistent with prevailing notions of health decline, our findings suggest that later life functional health, as captured in survey data, is more aptly characterized as a punctuated equilibrium: long-term stability that is irregularly interrupted by changes in health status or mortality. We conclude by discussing the implications of a punctuated equilibrium model for studies of health and aging.
Key words: health, aging, longitudinal analysis, trajectory