Mapping the 12-item multiple sclerosis walking scale to the EuroQol 5-dimension index measure in North American multiple sclerosis patients

Abstract

Objective To map the 12-item Multiple Sclerosis Walking Scale (MSWS-12) onto the EuroQol 5-dimension (EQ-5D) health-utility index in multiple sclerosis (MS) patients participating in the North American Research Committee on Multiple Sclerosis (NARCOMS) registry. Design Cross-sectional MSWS-12 to EQ-5D cross-walking analysis. Setting NARCOMS registry spring 2010 biannual update and supplemental survey. Participants North American patients completing both the MSWS-12 and the EQ-5D randomly split into derivation and validation cohorts. Outcome measures Ordinary least squares regression was performed within the derivation cohort, with participants’ EQ-5D as the dependent variable. Results of the MSWS-12 were input as independent variable(s) into six regression models. Model goodness-of-fit was subsequently assessed in the validation cohort using the mean absolute error (MAE), root mean square error (RMSE) and the adjusted R². The best performing model was refined in the entire cohort and utilised for additional analyses. Results A total of 3505 NARCOMS participants were included. Their mean±SD EQ-5D and MSWS-12 scores were 0.74±0.18 and 50.8±33.5, respectively, and these assessments were found to be moderately correlated (r=–0.553, p2=0.329). The percentage of EQ-5D estimates within 0.05 and 0.10 of the actual value were 30% and 61%, respectively. This mapping equation was more precise in patients with moderate mobility impairment (MAE=0.087±0.061 at patient-determined disease step (PDDS) of 3–6) and less precise in patients with no (MAE=0.141±0.128 at PDDS of 0–2) or severe mobility impairment (MAE=0.121±0.049 at PDDS ≥7). Conclusions The EQ-5D scores can be predicted using the MSWS-12 item scores with reasonable precision in North American patients with MS. Prediction estimates were more precise in patients with moderate mobility impairment.