title: Preference Weighting of Health State Values: What Difference Does It Make, and Why?
abstract: BACKGROUND
  Most patient-reported outcome measures apply a simple summary score to assess health-related quality of life, whereby equal weight is normally assigned to each item. In the generic preference-based instruments, utility weighting is essential whereby health state values are estimated through preference elicitation and complex algorithms.
  
  
  OBJECTIVE
  To examine the extent to which preference-weighted value sets differ from unweighted values in the five-level EuroQol five-dimensional questionnaire and the 15D instrument, on the basis of a comprehensive data set from six member countries of the Organisation for Economic Co-operation and Development, each with a representative healthy sample and seven disease groups (N = 7933).
  
  
  METHODS
  Construct validities were examined. The level of agreement between preference-weighted and unweighted values was also assessed using intraclass correlation coefficient (ICC), Bland-Altman plots, and reduced major axis regression.
  
  
  RESULTS
  The performances of preference-weighted and unweighted measures were comparable with regard to convergent and known-group validities for each instrument. Although unweighted values in the five-level EuroQol five-dimensional questionnaire differ considerably from the preference-weighted values at the individual level, the discrepancy is minimal at the group level with a mean difference of 0.023. The ICC (0.96) and the Bland-Altman plot also suggest strong overall agreement. For the 15D, both the ICC (0.99) and the Bland-Altman plot revealed almost perfect agreement, with a negligible mean difference of -0.001. Results from the reduced major axis regression also showed small bias.
  
  
  CONCLUSIONS
  Overall, preference weighting has minimal effect if the unweighted values are anchored on the same scale as the preference-weighted value sets.
authors.affiliation: Department of Community Medicine, University of Tromsø, Tromsø, Norway. Electronic address: admassu.n.lamu@uit.no.
authors.forename: Admassu N
authors.initials: AN
authors.lastname: Lamu
authors.affiliation: Department of Community Medicine, University of Tromsø, Tromsø, Norway.
authors.forename: Thor
authors.initials: T
authors.lastname: Gamst-Klaussen
authors.affiliation: Department of Community Medicine, University of Tromsø, Tromsø, Norway; Centre for Health Economics, Monash University, Clayton, VIC 3800, Australia.
authors.forename: Jan Abel
authors.initials: JA
authors.lastname: Olsen
mesh_terms: D001315:Australia; D002170:Canada; D005858:Germany; D006304:Health Status; D006305:Health Status Indicators; D006801:Humans; D009664:Norway; D066150:Organisation for Economic Co-Operation and Development; D011594:Psychometrics; D011788:Quality of Life; D012044:Regression Analysis; D015203:Reproducibility of Results; D018434:Sickness Impact Profile; D011795:Surveys and Questionnaires / Q000592:standards*; D006113:United Kingdom; D014481:United States; D064232:Visual Analog Scale
keywords: 15D; EQ-5D-5L; health-related quality of life; preference weighting