title: Mapping chronic liver disease questionnaire scores onto SF-6D utility values in patients with primary sclerosing cholangitis.
abstract: OBJECTIVE
  The chronic liver disease questionnaire (CLDQ) is a frequently used liver-specific quality of life instrument, but it does not provide information on preference-adjusted health status, which is essential for cost-utility analysis. We aimed to develop a mapping function deriving utilities from the CLDQ in primary sclerosing cholangitis (PSC).
  
  
  METHODS
  Short form-6D (SF-6D) utilities were calculated from SF-36 data collected in a recent prospective study in which unselected patients with PSC also completed the CLDQ. Ordinary least squares (OLS), generalized linear, median, and kernel regression analyses were employed to devise a mapping function predicting utilities. This was validated in three random subsamples of the cohort and in a separate sample of PSC patients following liver transplantation. Adjusted R (2) and root-mean-square error (RMSE) as well as Pearson's r coefficients and mean absolute errors between predicted and observed values were used to determine model performance.
  
  
  RESULTS
  Decompensated liver disease and fatigue, systemic symptoms, and emotional distress, assessed with the CLDQ, were related to worse SF-6D utilities. The final OLS prediction model explained 66.3 % of the variance in the derivation sample. Predicted and observed utilities were strongly correlated (r = 0.807, p < 0.001), but the mean absolute error (0.0604) and adjusted RMSE (10.6 %) were of intermediate size. Similar model characteristics were observed after employment of generalized linear and median regression models and at validation.
  
  
  CONCLUSIONS
  A model has been constructed, showing good validity predicting SF-6D utilities from CLDQ scores at the group level in PSC. Further testing is required to externally validate the model.
authors.affiliation: Digestive Disease Center, Copenhagen University Hospital/Bispebjerg, University of Copenhagen, 2400, Copenhagen, Denmark. kalvag@hotmail.com.|Institute of Internal Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden. kalvag@hotmail.com.|Faculty of Social Sciences, Hellenic Open University, Patras, Greece. kalvag@hotmail.com.
authors.forename: Evangelos
authors.identifier: http://orcid.org/0000-0002-9947-8914
authors.initials: E
authors.lastname: Kalaitzakis
authors.affiliation: Institute of Internal Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Maria
authors.initials: M
authors.lastname: Benito de Valle
authors.affiliation: Department of Gastroenterology, John Radcliffe Hospital, Oxford, UK.
authors.forename: Monira
authors.initials: M
authors.lastname: Rahman
authors.affiliation: Institute of Internal Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Björn
authors.initials: B
authors.lastname: Lindkvist
authors.affiliation: Department of Internal Medicine, Landspitali University Hospital, Reykjavik, Iceland.
authors.forename: Einar
authors.initials: E
authors.lastname: Björnsson
authors.affiliation: Department of Gastroenterology, John Radcliffe Hospital, Oxford, UK.
authors.forename: Roger
authors.initials: R
authors.lastname: Chapman
authors.affiliation: Faculty of Social Sciences, Hellenic Open University, Patras, Greece.
authors.forename: Nick
authors.initials: N
authors.lastname: Kontodimopoulos
mesh_terms: D000465:Algorithms; D015209:Cholangitis, Sclerosing / Q000523:psychology* / Q000601:surgery; D003362:Cost-Benefit Analysis; D005260:Female; D006304:Health Status; D006801:Humans; D016018:Least-Squares Analysis; D008107:Liver Diseases / Q000523:psychology* / Q000601:surgery; D016031:Liver Transplantation; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D011446:Prospective Studies; D011788:Quality of Life / Q000523:psychology*; D011795:Surveys and Questionnaires
keywords: Chronic liver disease questionnaire; Health utilities; Health-related quality of life; Liver transplantation; Mapping; Primary sclerosing cholangitis; SF-6D