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

Background and Objectives: 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) . Research Design and Methods: 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: 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). Discussion and Implications: 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.