Metric attributes of the unified Parkinson's disease rating scale 3.0 battery: Part I, feasibility, scaling assumptions, reliability, and precision.

This article sought to assess the feasibility, scaling assumptions, reliability, precision, and factor analysis of the three most widely used rating scales in Parkinson's disease (PD): modified Hoehn and Yahr (HY), Schwab and England (SE), and Unified Parkinson's Disease Rating Scale (UPDRS). A multicenter sample of 1,136 PD patients was assessed. The percentage of missing data was 8% for SE, HY, and UPDRS mentation, and almost negligible (<2%) for the other UPDRS subscales. A high floor effect was found for UPDRS mentation (23%) and complications scales (36%). Item content validity, measured by multitrait scaling analysis, was adequate for all UPDRS subscales (scaling successes > 90%). Internal consistency coefficients for the UPDRS scales ranged from 0.79 (mentation) to 0.92 (activities of daily living and motor). Factor structure of the UPDRS mentation, activities of daily living, and complications subscales was replicated. As a whole, the HY, SE, and UPDRS are acceptable, consistent, and potentially sensitive rating scales.