Abstract
BACKGROUND: By including categories for accommodations and reduced frequency, to supplement earlier classifications of difficulty and dependence, a new 5-category functional scale has the potential to distinguish finer gradations in disability but the hierarchical nature and advantages of this scale over alternative scales are uncertain. METHODS: Using data from the National Health and Aging Trends Study (N = 7,609), we conducted a series of: cross-sectional analyses that focused on the hierarchical consistency of responses in the 5-category scale; and longitudinal analyses that focused on predictive accuracy for mortality and functional dependence, comparing the 5-category scale with three simpler scales, having only three or four categories. RESULTS: Although there was considerable variability across the seven functional activities, the prevalence of inconsistencies in the hierarchy of the 5-category scale (eg, reports difficulty but no accommodations) was relatively high. In addition, the predictive accuracy of the 5-category scale for mortality and functional dependence was only modestly better than that of the two 3-category scales and was comparable to that of the 4-category scale. Finally, when evaluated as summative disability scores, there was little difference in predictive accuracy between the 5-category scale and three alternative scales. CONCLUSIONS: Despite inconsistencies in its hierarchy, the 5-category scale is more effective in stratifying risk for mortality and functional dependence than the two 3-category scales but not the 4-category scale. When assessing changes over time, however, the addition of questions on accommodations and reduced frequency to those on difficulty and dependence, to form a summative disability score, offers little benefit and increases the burden of the assessment.