title: Estimating a Preference-Based Index for an Eight-Dimensional Health State Classification System for Multiple Sclerosis.
abstract: BACKGROUND
  Condition-specific measures are frequently used to assess the health-related quality of life of people with multiple sclerosis (MS). Such measures are unsuitable for use in economic evaluations that require estimates of cost per quality-adjusted life-year because they are not based on preferences.
  
  
  OBJECTIVE
  To report the estimation of a preference-based single index for an eight-dimensional instrument for MS, the Multiple Sclerosis Impact Scale - Eight Dimensions (MSIS-8D), derived from an MS-specific measure of health-related quality of life, the 29-item Multiple Sclerosis Impact Scale (MSIS-29).
  
  
  METHODS
  We elicited preferences for a sample of MSIS-8D states (n = 169) from a sample (n = 1702) of the UK general population. Preferences were elicited using the time trade-off technique via an Internet-based survey. We fitted regression models to these data to estimate values for all health states described by the MSIS-8D. Estimated values were assessed against MSIS-29 scores and values derived from generic preference-based measures in a large, representative sample of people with MS.
  
  
  RESULTS
  Participants reported that the time trade-off questions were easy to understand. Observed health state values ranged from 0.08 to 0.89. The best-performing model was a main effects, random effects model (mean absolute error = 0.04). Validation analyses support the performance of the MSIS-8D index: it correlated more strongly than did generic measures with MSIS-29 scores, and it discriminated effectively between subgroups of people with MS.
  
  
  CONCLUSIONS
  The MSIS-8D enables health state values to be estimated from the MSIS-29, adding to the methods available to assess health outcomes and to estimate quality-adjusted life-years for MS for use in health technology assessment and decision-making contexts.
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; UK National Institute for Health Research (NIHR) Collaboration for Leadership in Applied Health Research and Care of the South West Peninsula (PenCLAHRC), University of Exeter Medical School, University of Exeter, Exeter, UK.
authors.forename: Colin
authors.initials: C
authors.lastname: Green
authors.affiliation: Health Economics Group, University of Exeter Medical School, University of Exeter, Exeter, UK.
authors.forename: Anne
authors.initials: A
authors.lastname: Spencer
mesh_terms: D000203:Activities of Daily Living; D006305:Health Status Indicators; D006801:Humans; D007398:Interpersonal Relations; D008603:Mental Health; D051346:Mobility Limitation; D009103:Multiple Sclerosis / Q000523:psychology*; D057240:Patient Preference; D011788:Quality of Life; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires; D013997:Time Factors
keywords: multiple sclerosis; preference-based measures; quality-adjusted life-years