Purpose: To examine the psychometric properties of six outcome measures in people with Parkinson disease (PD).
Method: Twenty-four participants completed the following twice within 2 weeks: the timed up-and-go test (TUG), Northwestern University Disability Scale (NUDS), Schwab & England ADL Scale (S&E), Activities-specific Balance Confidence (ABC) Scale, PD Questionnaire—Short Form (PDQ 8), and Stanford Self-Efficacy for Managing Chronic Disease 6-Item Scale (SSE). Internal consistency, test–retest reliability (ICC[3,1]), and minimal detectable change (MDC) scores were calculated. Convergent and discriminant validity of the ABC were examined.
Results: Cronbach's alpha scores for the NUDS, ABC, PDQ-8, and SSE were 0.47, 0.92, 0.72, and 0.91 respectively. The intra-class correlation coefficient (ICC[3,1]) for the TUG was 0.69 and could be improved by averaging two trials. ICCs for the NUDS, S&E, ABC, PDQ-8, and SSE were 0.56, 0.70, 0.79, 0.82, and 0.72 respectively. The ABC correlated with the TUG (r=−0.44, p=0.03) and with PDQ-8 (rs=0.51, p=0.01) and NUDS (rs=0.48, p=0.02) walking items. The ABC was able to discriminate between stages 1 and 3 of disease progression but not between stages 1 and 2, which suggests that the ABC can distinguish large differences in disease progression but cannot detect more subtle differences.
Conclusions: Homogeneity of the ABC, PDQ-8, and SSE is good to excellent. Test–retest reliability scores of all measures except the NUDS are moderate to good. The ABC is a valid measure for use in PD. The MDC statistic may be useful for interpreting group score changes.