Clinimetric analyses of the Modified Parkinson Activity Scale

The Parkinson Activity Scale (PAS) is designed for functional assessment in Parkinson's disease (PD), but the scale has - in its current form - several drawbacks. The objectives of the present study are to (a) introduce a Modified PAS, with unambiguous scoring options and without ceiling effect; (b) evaluate the inter-rater agreement, using physiotherapists with and without PD-specific expertise; and (c) examine the concurrent validity with the VAS-Global Functioning and the UPDRS-III.

The Modified PAS was developed based on the results of a recent pilot feasibility study [Keus SHJ, Bloem BR, van Hilten JJ, Ashburn A, Munneke M. Effectiveness of physiotherapy in Parkinson's disease: The feasibility of a randomised controlled trial. Parkinsonism Relat Disord 2007; 13(2):115-21.]. To evaluate inter-rater agreement, the Modified PAS was scored by a large number of raters (n=13) in 15 patients (Hoehn and Yahr stage 2-4), thus yielding a high number of observations (n=195) and creating adequate power. To ascertain broad applicability of the results, both physiotherapists with and without PD-specific expertise participated.

The interquartile range of the Modified PAS total scores was 40-51, within a possible range of 0 (optimal performance) to 56 (worst performance), suggesting lack of ceiling effect. The precision of these scores was 2.6 points, with an inter-rater error of 1.3 and a patient-induced error of 2.3. There were no differences between experts and non-experts. Correlation to Global Functioning (0.79) and UPDRS-III (0.64) was good.

The Modified PAS showed no ceiling effect, good concurrent validity, good inter-rater agreement and no differences between experts and non-experts.