Validity of performance scales for disability assessment in multiple sclerosis

Researchers increasingly use self-reported health status assessments, but these require validation. Performance Scales (PS) is a self-report measure for multiple sclerosis (MS)-associated disability, assessing mobility, bowel/bladder, fatigue, sensory, vision, cognition, spasticity and hand function. The criterion validity of the total PS score was established using the Expanded Disability Status Scale (EDSS), but the construct and criterion validity of the individual subscales have not been established. We assessed the criterion and construct validity of the PS subscales. Forty-four patients with MS completed PS, and these criterion measurements: neurological examination (EDSS), the Multiple Sclerosis Functional Composite (MSFC), contrast acuity testing, and the Multiple Sclerosis Quality of Life Inventory. We assessed criterion and construct validity with Spearman rank correlations between PS subscales and the other measurements. PS correlated with the MSFC (r= -0.58, P < 0.0001). The mobility, hand, vision, fatigue and bladder subscales correlated with their criterion measures (r= 0.59-0.77, P < 0.0001). The sensory subscale correlated weakly with the sensory functional system score (r = 0.39, P = 0.01), and the cognitive subscale did not correlate with the PASAT (r= -0.17, P = 0.26). This study supports the criterion and construct validity of PS overall, and its mobility, hand, vision, fatigue, and bladder subscales. Further assessment of the cognitive, sensory and spasticity subscales is needed.