Gradual Change, Homeostasis, and Punctuated Equilibrium: Reconsidering Patterns of Health in Later Life

Abstract

Longitudinal methods aggregate individual health histories to produce inferences about aging populations, but to what extent do these summaries reflect the experiences of older adults? We describe the assumption of gradual change built into several influential statistical models and draw on widely used, nationally representative survey data to empirically compare the conclusions drawn from mixed-regression methods (growth curve models and latent class growth analysis) designed to capture trajectories with key descriptive statistics and methods (multistate life tables and sequence analysis) that depict discrete states and transitions. We show that individual-level data record stasis irregularly punctuated by relatively sudden change in health status or mortality. Although change is prevalent in the sample, for individuals it occurs rarely, at irregular times and intervals, and in a nonlinear and multidirectional fashion. We conclude by discussing the implications of this punctuated equilibrium pattern for understanding health changes in individuals and the dynamics of inequality in aging populations.

Deaths, Disparities, and Cumulative (Dis)Advantage: How Social Inequities Produce an Impairment Paradox in Later Life

“…Since the risk of death or attrition increases with both age and study duration, we consider loss to follow up and mortality as informative outcomes, consistent with the Punctuated Equilibrium approach ( 8 ). People are considered lost to follow up if they are not in sample for the last used round of the HRS (Wave 13) and do not have a date of death via the linked National Death Index.…”

“…We re-evaluate the salience of these factors for disparities in later-life health and mortality by moving away from the latent trajectory models most common in studies of health disparities toward a Punctuated Equilibrium modeling strategy ( 8 , 35 ). The latter explicitly incorporates both mortality and nonrandom attrition as competing risks for multidirectional health change via nonparametric methods and multinomial logistic regressions.…”

“…Such findings have puzzled scholars of cumulative (dis)advantage (CAD) ( 5–7 ) who expect prolonged exposures to structural racism and discrimination on the basis of gender, socioecononmic status, and other characteristics may manifest in widening health inequities throughout the life course. Using nationally representative data tracking older adults for over 2 decades and an analytic approach informed by the recently developed Punctuated Equilibrium modeling framework ( 8 ), we offer a new perspective on this puzzle.…”

Mobility, Stagnation, or Attrition? Diverse Earning Trajectories in a Cohort of Foreign‐born Men

“…Recent work on health and aging has found that nonrandom attrition and missingness in longitudinal surveys means that the “average trajectory” of health does not accurately reflect the health histories of most individuals (Engelman and Jackson 2019) and that common approaches to handling missingness in longitudinal analyses result in biased estimates (Jackson, Engelman, and Bandeen‐Roche 2019). Similarly, due to right‐ and left censoring and nonrandom missingness in earning records, the “average trajectory” of earnings in previous research may not accurately represent many immigrants’ earnings progression.…”

The Heterogeneity of Disability Trajectories in Later Life: Dynamics of Activities of Daily Living Performance Among Nursing Home Residents

“…Each of these approaches has potential limitations in fully capturing the heterogeneity in the evolution of functional health in later life. Mixed effect models for instance, although able to distinguish differences in the overall disability trend among groups, have an underlying hypothesis of gradual accumulation of functional limitation assuming a smooth functional form in the trajectories (Engelman & Jackson, 2017). Disability trajectories might instead show complex non-homogeneous behaviors (see Figure 1 in supplemental materials).…”