Test-retest reliability and minimal detectable change on balance and ambulation tests, the 36-item short-form health survey, and the unified Parkinson disease rating scale in people with parkinsonism

Teresa Steffen, Megan Seney
Physical Therapy 2008, 88 (6): 733-46

BACKGROUND AND PURPOSE: Distinguishing between a clinically significant change and change due to measurement error can be difficult. The purpose of this study was to determine test-retest reliability and minimal detectable change for the Berg Balance Scale (BBS), forward and backward functional reach, the Romberg Test and the Sharpened Romberg Test (SRT) with eyes open and closed, the Activities-specific Balance Confidence (ABC) Scale, the Six-Minute Walk Test (6MWT), comfortable and fast gait speed, the Timed "Up & Go" Test (TUG), the Medical

OUTCOMES: Study 36-Item Short-Form Health Survey (SF-36), and the Unified Parkinson Disease Rating Scale (UPDRS) in people with parkinsonism.

SUBJECTS: Thirty-seven community-dwelling adults with parkinsonism (mean age=71 years) participated. The Hoehn and Yahr Scale median score of 2 was on the lower end of the scale; however, the scores ranged from 1 to 4.

METHODS: Subjects were tested twice by the same raters, with 1 week between tests. Test-retest reliability was calculated using intraclass correlation coefficients (ICCs). Minimal detectable change was calculated using a 95% confidence interval (MDC(95)).

RESULTS: The ICCs for test-retest reliability were above .90 for the BBS, ABC Scale, SRT with eyes closed, 6MWT, and comfortable and fast gait speeds. The MDC(95) values for those functional tests were: BBS=5/56, ABC Scale=13%, SRT with eyes closed=19 seconds, 6MWT=82 m, comfortable gait speed=0.18 m/s, and fast gait speed=0.25 m/s. The ICCs for test-retest reliability of SF-36 scores were above .80, with the exception of the social functioning subscale. The MDC(95) values for the SF-36 ranged between 19% and 45%. The MDC(95) values for the UPDRS Activities of Daily Living section, Motor Examination section, and total scores were 4/52, 11/108, and 13/176, respectively.

DISCUSSION AND CONCLUSION: Minimal detectable change values are useful to therapists in rehabilitation and wellness programs in determining whether change during or after intervention is clinically significant. High test-retest reliability of scores for the BBS, ABC Scale, SRT with eyes closed, 6MWT, and gait speed make them trustworthy functional assessments in people with parkinsonism. The SF-36 and UPDRS provide quality-of-life and disease severity rating values in the ongoing assessment of people with parkinsonism.

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