title: Multi-group measurement invariance of the multiple sclerosis walking scale-12?
abstract: OBJECTIVE
  One primary assumption underlying the interpretation of composite multiple sclerosis walking scale-12 (MSWS-12) scores across levels of disability status is multi-group measurement invariance. This assumption was tested in the present study between  samples that differed in self-reported disability status.
  
  
  METHODS
  Participants (n = 867) completed a battery of questionnaires that included the MSWS-12 and patient-determined disease step (PDDS) scale. The multi-group invariance was tested between samples that had  PDDS scores of ≤2 (i.e. no mobility limitation; n = 470) and PDDS scores ≥3 (onset of mobility limitation; n = 397) using Mplus 6·0.
  
  
  RESULTS
  The omnibus test of equal covariance matrices indicated that the MSWS-12 was not invariant  between the two samples that differed in disability status. The source of non-invariance occurred with the initial equivalence test of the factor structure itself.
  
  
  CONCLUSIONS
  We provide evidence that questions the unambiguous interpretation of scores from the MSWS-12 as a measure  of walking impairment between samples of persons with multiple sclerosis who differ in disability status.
authors.affiliation: University of Illinois at Urbana-Champaign, Urbana, IL, USA. robmotl@illinois.edu
authors.forename: Robert W
authors.initials: RW
authors.lastname: Motl
authors.forename: Sean
authors.initials: S
authors.lastname: Mullen
authors.forename: Edward
authors.initials: E
authors.lastname: McAuley
mesh_terms: D004185:Disability Evaluation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D051346:Mobility Limitation; D009103:Multiple Sclerosis / Q000150:complications*; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires; D016138:Walking