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Test–Retest Reliability of Subclinical Status for Functional Limitation and Disability

¹ Center for Aging Research, Indiana University, and Regenstrief Institute, Inc., Indianapolis.
² Health Services R&D Service, Department of Veterans Affairs Medical Center, and College of Public Health and Health Professions, University of Florida, Gainesville.
³ Department of Psychiatry, School of Medicine, Saint Louis University, St. Louis, Missouri.
⁴ Division of Biostatistics, Washington University School of Medicine, St. Louis, Missouri.
⁵ College of Public Health, University of Iowa, and Iowa City VAMC, Iowa City.

Address correspondence to Douglas K. Miller, MD, IU Center for Aging Research, 1050 Wishard Blvd., RG-6, Indianapolis, IN 46202. E-mail: dokmille{at}iupui.edu

Objectives. Subclinical status for functional limitation and disability help explain pathways to difficulties with functional limitation and disability, but data on their measurement stability are minimal. We evaluated the reproducibility of measuring subclinical status in a random subset of 92 community-dwelling St. Louis African Americans aged 49 to 65 years old.

Methods. We examined test–retest reliability of subclinical status using Fried's measurement method of changing either the frequency or method of task performance for five functional limitations, three basic activities of daily living (ADLs), and four instrumental ADLs, as well as summary scales reflecting these three constructs. We also performed sensitivity analyses of test–retest interval and alternative definitional approaches (using only method, only frequency, or both).

Results. Weighted kappas for individual tasks across three performance levels (high functioning, subclinical status, and task difficulty) indicated moderate agreement for one task and substantial agreement for 11 tasks. Intraclass correlation coefficients for the three scales demonstrated outstanding agreement. The most reproducible definition of subclinical status involved the either/or method.

Discussion. Excellent test–retest reproducibility was demonstrated in this population-based sample of late middle-aged African Americans using Fried's method of measuring subclinical status.