Development and validation of a functional outcome measure in the national health and aging trends study

Abstract

Background: Despite the rich array of data available on seven self-care and mobility activities, a functional outcome measure, which sums the scores across these activities, has not yet been developed or validated for use in the National Health and Aging Trends Study (NHATS). Methods: Using longitudinal data from NHATS, we evaluted 7,609 participants who were living in community settings. Development of the functional outcome measure was guided by the presence of consistent mortality gradients across a 5-category, 4-category, and two 3-category scales for each of the seven activities, whereas validation was based on predictive accuracy for mortality and concurrent change in physical performance. Results: Consistent mortality gradients were observed only for the two 3-category scales (with each activity scored as 1 [fully able/independent], 2 [vulnerable], or 4 [assistance]). Each version of the corresponding functional outcome measure, which had a range of composite scores from 7 (no disability) to 28 (highest disability), demonstrated strong predictive validity for mortality and concurrent change in physical performance, with a 2-point change being clinically meaningful. The version that defned vulnerability on the basis of accommodations, reduced activities, or diffculty, rather than diffculty alone, is preferable for use in NHATS based on a more even distribution of composite scores, a wider and more consistent mortality gradient without any mortality reversals, and slightly stronger associations with the two outcomes. Conclusions: These results provide strong, albeit preliminary evidence supporting the value of a new functional outcome measure for use in NHATS, a rich resource for investigating late-life disability.