title: A Quality-Adjusted Life-Year Measure for Multiple Sclerosis: Developing a Patient-Reported Health State Classification System for a Multiple Sclerosis-Specific Preference-Based Measure.
abstract: BACKGROUND
  Increasingly, generic preference-based measures of health-related quality of life (HRQOL) are used to estimate quality-adjusted life-years to inform resource allocation decisions. Evidence suggests that generic measures may not be appropriate for multiple sclerosis (MS).
  
  
  OBJECTIVE
  To report the first stage in the development of an MS-specific preference-based measure to quantify the impact of MS and its treatment: deriving a health state classification system, which is amenable to valuation, from the 29-item Multiple Sclerosis Impact Scale (MSIS-29), a widely used patient-reported outcome measure in MS.
  
  
  METHODS
  The dimensional structure of the MSIS-29 was determined using factor analysis and a conceptual framework of HRQOL in MS. Item performance was assessed, using Rasch analysis and psychometric criteria, to enable the selection of one item to represent each dimension of HRQOL covered by the MSIS-29. Analysis was undertaken using a sample (N = 529) from a longitudinal study of people with MS. Results were validated by repeating the analysis with a second sample (N = 528).
  
  
  RESULTS
  Factor analysis confirmed the two-subscale structure of the MSIS-29. Both subscales covered several conceptually independent dimensions of HRQOL. Following Rasch and psychometric analysis, an eight-dimensional classification system named the MSIS-8D was developed. Each dimension was represented by one item with four response levels.
  
  
  CONCLUSIONS
  Combining factor analysis with conceptual mapping, and Rasch analysis with psychometric criteria, provides a valid method of constructing a classification system for an MS-specific preference-based measure. The next stage is to obtain preference weights so that the measure can be used in studies investigating MS.
authors.affiliation: Health Economics Group, University of Exeter Medical School, University of Exeter, Exeter, UK. Electronic address: e.goodwin@exeter.ac.uk.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Goodwin
authors.affiliation: Health Economics Group, University of Exeter Medical School, University of Exeter, Exeter, UK; Collaboration for Leadership in Applied Health Research and Care South West Peninsula, University of Exeter Medical School, University of Exeter, Exeter, UK.
authors.forename: Colin
authors.initials: C
authors.lastname: Green
mesh_terms: D000223:Adaptation, Psychological; D000328:Adult; D005163:Factor Analysis, Statistical; D005260:Female; D006304:Health Status; D006305:Health Status Indicators; D006801:Humans; D007398:Interpersonal Relations; D008137:Longitudinal Studies; D008297:Male; D008603:Mental Health; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000150:complications / Q000523:psychology*; D011788:Quality of Life; D019057:Quality-Adjusted Life Years; D015203:Reproducibility of Results; D057566:Self Report
keywords: Rasch analysis; health states; health-related quality of life; multiple sclerosis; preference-based measures of health; quality-adjusted life-years