Background: The minimal detectable change (MDC) is the smallest amount of difference in individual scores that represents true change (beyond random measurement error). The MDCs of the Timed "Up & Go" Test (TUG) and the Dynamic Gait Index (DGI) in people with Parkinson disease (PD) are largely unknown, limiting the interpretability of the change scores of both measures.
Objective: The purpose of this study was to estimate the MDCs of the TUG and the DGI in people with PD.
Design: This investigation was a prospective cohort study.
Methods: Seventy-two participants were recruited from special clinics for movement disorders at a university hospital. Their mean age was 67.5 years, and 61% were men. All participants completed the TUG and the DGI assessments twice, about 14 days apart. The MDC was calculated from the standard error of measurement. The percentage MDC (MDC%) was calculated as the MDC divided by the mean of all scores for the sample. Furthermore, the intraclass correlation coefficient was used to examine the reproducibility between testing sessions (test-retest reliability).
Results: The respective MDC and MDC% of the TUG were 3.5 seconds and 29.8, and those of the DGI were 2.9 points and 13.3. The test-retest reliability values for the TUG and the DGI were high; the intraclass correlation coefficients were .80 and .84, respectively.
Limitations: The study sample was a convenience sample, and the participants had mild to moderately severe PD.
Conclusions: The results showed that the TUG and the DGI have generally acceptable random measurement error and test-retest reliability. These findings should help clinicians and researchers determine whether a change in an individual patient with PD is a true change.