title: Development of a transformation model to derive general population-based utility: Mapping the pruritus-visual analog scale (VAS) to the EQ-5D utility.
abstract: OBJECTIVE
  Although nonpreference-based disease-specific measures are widely used in clinical studies, they cannot generate utilities for economic evaluation. A solution to this problem is to estimate utilities from disease-specific instruments using the mapping function. This study aimed to develop a transformation model for mapping the pruritus-visual analog scale (VAS) to the EuroQol 5-Dimension 3-Level (EQ-5D-3L) utility index in pruritus.
  
  
  METHODS
  A cross-sectional survey was conducted with a sample (n = 268) drawn from the general population of South Korea. Data were randomly divided into 2 groups, one for estimating and the other for validating mapping models. To select the best model, we developed and compared 3 separate models using demographic information and the pruritus-VAS as independent variables. The predictive performance was assessed using the mean absolute deviation and root mean square error in a separate dataset.
  
  
  RESULTS
  Among the 3 models, model 2 using age, age squared, sex, and the pruritus-VAS as independent variables had the best performance based on the goodness of fit and model simplicity, with a log likelihood of 187.13. The 3 models had similar precision errors based on mean absolute deviation and root mean square error in the validation dataset. No statistically significant difference was observed between the mean observed and predicted values in all models.
  
  
  CONCLUSIONS
  In conclusion, model 2 was chosen as the preferred mapping model. Outcomes measured as the pruritus-VAS can be transformed into the EQ-5D-3L utility index using this mapping model, which makes an economic evaluation possible when only pruritus-VAS data are available.
authors.affiliation: School of Pharmacy, Sungkyunkwan University, Suwon, South Korea.
authors.forename: Sun-Young
authors.identifier: http://orcid.org/0000-0003-3336-1681
authors.initials: SY
authors.lastname: Park
authors.affiliation: Department of Research Center for Drug Policy, Korea Institute for Health and Social Affairs, Seoul, South Korea.
authors.forename: Eun-Ja
authors.initials: EJ
authors.lastname: Park
authors.affiliation: College of Pharmacy, Pusan National University, Busan, South Korea.
authors.forename: Hae Sun
authors.initials: HS
authors.lastname: Suh
authors.affiliation: School of Pharmacy, Sungkyunkwan University, Suwon, South Korea.
authors.forename: Dongmun
authors.initials: D
authors.lastname: Ha
authors.affiliation: School of Pharmacy, Sungkyunkwan University, Suwon, South Korea.
authors.forename: Eui-Kyung
authors.initials: EK
authors.lastname: Lee
mesh_terms: D000328:Adult; D000367:Age Factors; D003362:Cost-Benefit Analysis; D003430:Cross-Sectional Studies; D005260:Female; D006304:Health Status; D006801:Humans; D008297:Male; D008875:Middle Aged; D011537:Pruritus / Q000503:physiopathology / Q000523:psychology*; D011594:Psychometrics; D011788:Quality of Life / Q000523:psychology*; D015203:Reproducibility of Results; D056910:Republic of Korea; D012720:Severity of Illness Index; D012737:Sex Factors; D012959:Socioeconomic Factors; D011795:Surveys and Questionnaires / Q000592:standards*
keywords: EQ-5D; economic evaluation; mapping; pruritus; pruritus-VAS; utility