Measuring Activity Limitations Within the National Health and Aging Trends Study (NHATS).

Abstract

To better understand the disablement process among older adults, improved measures of activity limitations are needed. Traditional population-level measures lack the ability to distinguish precise gradations of activity limitation and are unable to detect degrees of differences over a wide range of ability levels. Therefore, we used contemporary measurement methods to improve upon current methodologies for characterizing activity limitations within the National Health and Aging Trends Study (NHATS) . We used the NHATS Round 1 cohort to assess the feasibility of constructing an Activity Limitations scale using Rasch item response theory methods. Factor analysis was used to develop the scale from a set of existing items in the NHATS Mobility, Self-Care, and Household Activity domains. Psychometric properties of the scale were evaluated and the scale was used to examine change in activity limitations among the sample from 2011 to 2015. Results supported an 18-item scale (N = 7,609). Rasch infit and outfit statistics were within acceptable range for all items (Cronbach's alpha = 0.95; sample score reliability = 0.83). From 2011 to 2015, 5.88% older adults demonstrated increase in function, 15% showed decrease in function, and 78% of the sample showed no change (did not exceed ± MDC90). Findings demonstrate that a unidimensional, interval scale of activity limitations can be constructed using traditional survey measures nested within the NHATS. Results revealed concerns regarding ceiling effects within the current self-report items of activity limitations suggesting future work is needed to expand the range of ability currently represented in the NHATS Activity Limitation items.