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

Abstract

ObjectiveTo 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.DesignCross-sectional MSWS-12 to EQ-5D cross-walking analysis.SettingNARCOMS registry spring 2010 biannual update and supplemental survey.ParticipantsNorth American patients completing both the MSWS-12 and the EQ-5D randomly split into derivation and validation cohorts.Outcome measuresOrdinary 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.ResultsA 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, p<0.001). The model using all individual MSWS-12 item scores as independent variables was found to have the best fit (MAE=0.109±0.096, RMSE=0.145, adjusted R2=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).ConclusionsThe 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.

Mapping of Multiple Sclerosis Walking Scale (MSWS-12) to five-dimension EuroQol (EQ-5D) health outcomes: an independent validation in a randomized control cohort

“…Results of this analysis suggest that the previously derived and validated mapping equation using each individual item of the MSWS-12 predicted EQ-5D-3L values in the DER-401 cohort with similar precision as in the original NARCOMS cohort. 8 Notably, the differences between MAE and RMSE values were small, indicating only low variance for the individual errors in the sample. Moreover, visual inspection of the MAE and RMSE values combined with the subgroup analysis that stratified patients by observed EQ-5D-3L values suggested that the mapping equation performed best among patients with moderate EQ-5D-3L health-state values (ie, EQ-5D-3L scores 0.50–0.75) and performed less optimally in patients with more severe health states (ie, EQ-5D-3L scores <0.50).…”

“…In addition to the validation study in the NARCOMS population, 8 two other studies have been published that mapped MSWS-12 to EQ-5D-3L. 15 , 16 Hawton et al 15 developed a mapping equation from a sample of MS patients in the UK and using the UK scoring algorithm for the EQ-5D.…”

“… 13 These recommendations support the use of an external sample to validate mapping equations. At the time of the original mapping study, 8 no external population was available. Instead, the NARCOMS cohort was randomly split into derivation and validation cohorts, with the final equation refined using the entire cohort.…”

“…This mapping equation was derived using over 3,500 participants (mean EQ-5D-3L and MSWS-12 scores 0.74±0.18 and 50.8±33.5, respectively) in the NARCOMS registry using ordinary least squares regression. 8 The equation EQ-5D-3L = 0.002× (item 1) −0.009× (item 2) −0.01× (item 3) −0.029× (item 4) −0.019× (item 5) −0.0000881× (item 6) −0.008× (item 7) −0.002× (item 8) +0.013× (item 9) −0.011× (item 10) +0.001× (item 11) −0.008× (item 12) +0.983 uses all of the individual MSWS-12 item scores to estimate EQ-5D-3L index scores with a mean absolute error (MAE) of 0.109±0.096. These predicted EQ-5D-3L values were then compared to observed EQ-5D-3L values from DER-401 using the actual EQ-5D-3L health-status index questionnaire.…”

“…An equation to map the MSWS-12 onto the EQ-5D-3L health-utility index in North American patients with MS has been developed. 8 This equation, which was derived and validated in >3,500 MS patients from the North American Research Committee on MS (NARCOMS) registry, has been shown to predict EQ-5D-3L scores using individual MSWS-12 item scores with reasonable precision, especially in patients with moderate disease severity. Unfortunately, due to a lack of availability of another independent North American or US data set for MS patients that contains both the MSWS-12 and the EQ-5D-3L, the equation has never been further validated.…”