Evaluating Convergence of Within-Person Change and Between-Person Age Differences in Age-Heterogeneous Longitudinal Studies

Abstract

The distinction of between-person age differences from within-person age changes is necessary for understanding aging-related change processes. Although longitudinal studies are required to address issues relating to within-person change, most studies begin using age-heterogeneous samples and conclude using survival-heterogeneous samples. Given the numerous potential confounds associated with age-heterogeneous samples, careful treatment of between-person age differences is essential to obtain the correct inferences regarding within-person age change. The authors demonstrate how failure to differentiate between-person age effects (and by extension, of survival age or other effects producing sample heterogeneity) will lead to uninterpretable inferences regarding within-person change. The authors recommend that convergence of age differences and age changes be formally evaluated whenever possible.

ACKNOWLEDGMENT

This work was partially supported by National Institutes of Health (NIH) Grants R01 AG12448 and AG026728 and Integrative Analysis of Longitudinal Studies of Aging (IALSA) research network funded by NIH grant R01 AG026453.