Psychometric Properties of 3 Functional Mobility Tests for People With Parkinson Disease

Background Standardized outcome measures with high clinical utility are of paramount importance for clinical practice. Objective The purpose of this study was to examine interrater and intrarater reliability, construct validity, discriminant ability, and smallest detectable differences of the sit-to-stand test (STS), Timed “Up & Go” Test (TUG), and bed mobility test for people with Parkinson disease (PD). Design A cross-sectional, psychometric evaluation study was conducted. Methods A group of individuals with PD (PD group) and a group of individuals who were healthy (control group) were recruited through local PD groups and assessed in a movement laboratory in their “on” phase. Measurements of time to perform one STS, TUG, and bed mobility test were collected based on video recordings of that single performance. Results Thirty-eight individuals with PD (Hoehn and Yahr stages I–IV) and 19 age-matched control participants were recruited. Intraclass correlation coefficients for interrater and intrarater reliability for the PD group ranged from .95 to .99. Bland-Altman plots showed mean differences close to zero and narrow confidence intervals. Construct validity was established by means of moderate to good Spearman rho correlation coefficients with part III of the Unified Parkinson's Disease Rating Scale and the Hoehn and Yahr stage (range=.51–.63). Timings of all tests discriminated participants in the PD group from those in the control group and participants in the PD group in Hoehn and Yahr stages I and II from those in Hoehn and Yahr stages III and IV but did not discriminate “nonfallers” or those with single falls from repeat “fallers” or “nonfreezers” from “freezers.” Applicable smallest detectable differences were established. Limitations The results are not generalizable to people in the late stage of PD (Hoehn and Yahr stage IV: n=3). Conclusions Timings of video recordings of 3 functional mobility tests with high clinical utility showed good psychometric properties for community-dwelling, ambulatory people with PD.