title: The e-MSWS-12: improving the multiple sclerosis walking scale using item response theory.
abstract: The Multiple Sclerosis Walking Scale (MSWS-12) is the predominant patient-reported measure of multiple sclerosis (MS) -elated walking ability, yet it had not been analyzed using item response theory (IRT), the emerging standard for patient-reported outcome (PRO) validation. This study aims to reduce MSWS-12 measurement error and facilitate computerized adaptive testing by creating an IRT model of the MSWS-12 and distributing it online.
  
  
  
  MSWS-12 responses from 284 subjects with MS were collected by mail and used to fit and compare several IRT models. Following model selection and assessment, subpopulations based on age and sex were tested for differential item functioning (DIF).
  
  
  
  Model comparison favored a one-dimensional graded response model (GRM). This model met fit criteria and explained 87 % of response variance. The performance of each MSWS-12 item was characterized using category response curves (CRCs) and item information. IRT-based MSWS-12 scores correlated with traditional MSWS-12 scores (r = 0.99) and timed 25-foot walk (T25FW) speed (r =  -0.70). Item 2 showed DIF based on age (χ2= 19.02, df = 5, p < 0.01), and Item 11 showed DIF based on sex (χ2= 13.76, df = 5, p = 0.02).
  
  
  
  MSWS-12 measurement error depends on walking ability, but could be lowered by improving or replacing items with low information or DIF. The e-MSWS-12 includes IRT-based scoring, error checking, and an estimated T25FW derived from MSWS-12 responses. It is available at https://ms-irt.shinyapps.io/e-MSWS-12 .
authors.affiliation: Department of Systems and Information Engineering, University of Virginia, P.O. Box 400747, Charlottesville, VA, 22904, USA. mme@virginia.edu.
authors.forename: Matthew M
authors.initials: MM
authors.lastname: Engelhard
authors.affiliation: Department of Psychology, University of Virginia, P.O. Box 400400, Charlottesville, VA, 22904, USA.
authors.forename: Karen M
authors.initials: KM
authors.lastname: Schmidt
authors.affiliation: College of Arts and Sciences, University of Virginia, P.O. Box 400133, Charlottesville, VA, 22904, USA.
authors.forename: Casey E
authors.initials: CE
authors.lastname: Engel
authors.affiliation: Department of Neurology, University of Virginia, P.O. Box 800394, Charlottesville, VA, 22908, USA.
authors.forename: J Nicholas
authors.initials: JN
authors.lastname: Brenton
authors.affiliation: Department of Systems and Information Engineering, University of Virginia, P.O. Box 400747, Charlottesville, VA, 22904, USA.
authors.forename: Stephen D
authors.initials: SD
authors.lastname: Patek
authors.affiliation: Department of Neurology, University of Virginia, P.O. Box 800394, Charlottesville, VA, 22908, USA.
authors.forename: Myla D
authors.initials: MD
authors.lastname: Goldman
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000628:therapy*; D018434:Sickness Impact Profile; D016138:Walking / Q000502:physiology*
keywords: 12-Item multiple sclerosis walking scale; Differential item functioning; Graded response model; Item response theory; Multiple sclerosis; Timed 25-foot walk