RELIABILITY OF PHYSICAL PERFORMANCE AND SELF-REPORTED FUNCTIONAL MEASURES IN AN OLDER POPULATION

Background. Functional assessments and direct measures of physical per formance are standard components of community-based studies of older p opulations. Estimates of the reliability of these measures are necessa ry for the assessment of functional change. Methods. The reproducibili ty of 13 measures of self-reported function and 11 direct measures of physical performance was assessed. A sample of subjects (N = 199; grea ter than or equal to 55 yrs) was selected from a larger population-bas ed cohort. Subjects were tested in their homes twice, 48 hours apart, by the same interviewer to replicate study conditions. Age-adjusted ka ppa statistics were used to assess the reliability of measures of phys ical function; product moment correlation (Pearson r) and intraclass c orrelation coefficients (ICC) were used Lo assess direct measures of p erformance. A repeated measures model was used to assess learning or p ractice effects of performance, adjusted for age, sex, general health, and cognitive function. Results. Age-adjusted kappa statistics were g reater than or equal to.60 for most self-reported items. ICC ranged fr om .63 to .92. Significant improvements (practice effects) were found for the chair stand, walking speed, and the 360 degrees turn. Measures of grip strength, reaching down, and hand dexterity were found to be reliable, with no significant test effect. Conclusion. Three commonly used measures (chair stand, walking speed, and 360 degrees turn) may b e less reliable than previously reported. Sample sizes that may be nee ded to detect change in these areas of performance may be larger than previously estimated given this level of imprecision. Future studies o f reproducibility should assess both the level of agreement and the pr esence of possible practice effects.