Measuring Physical Capacity: An Assessment of a Composite Measure Using Self-Report and Performance-Based Items. (March 2017)

• Record Type: Journal Article
• Authors: Kasper, Judith D.; Chan, Kitty S.; Freedman, Vicki A.
• Is Part Of: Journal of aging and health. Volume 29:Number 2(2017:Mar.)
• Page Start: 289
• Page End: 309
• Publication Date: 2017-03
• Subjects: physical capacity -- physical function -- measurement -- performance tests -- self-reported function; Older people -- Health and hygiene -- Periodicals; Geriatrics -- Periodicals; 618.97
• DOI: 10.1177/0898264316635566
• Languages: English
• ISSNs: 0898-2643

Abstract

Objective: The objective of this study was to develop and assess a composite measure of physical capacity using self-report and physical performance items.Method: Item response theory (IRT) is used to evaluate measurement properties of self-report and performance items and to develop a composite measure for 7, 609 participants in the National Health and Aging Trends Study.Results: Self-reports distinguish differences at the lower end of physical capacity but not at mid-to-high levels. Performance-based measures discriminate across a fuller spectrum. An IRT-based composite score, drawing on both, provides increased measurement precision across the physical capacity spectrum and detects age group differences if either self-report or performance does so—suggesting it is better suited for studying age-related changes than either measure alone.Discussion: Self-report and performance measures have different strengths on the physical capacity spectrum. IRT provides a means of combining these different measurement approaches for analyses of physical capacity across a broad range of functioning in later life.