title: Mapping the EQ-5D index by UPDRS and PDQ-8 in patients with Parkinson's disease.
abstract: BACKGROUND
  Clinical studies employ the Unified Parkinson's Disease Rating Scale (UPDRS) to measure the severity of Parkinson's disease. Evaluations often fail to consider the health-related quality of life (HrQoL) or apply disease-specific instruments. Health-economic studies normally use estimates of utilities to calculate quality-adjusted life years. We aimed to develop an estimation algorithm for EuroQol- 5 dimensions (EQ-5D)-based utilities from the clinical UPDRS or disease-specific HrQoL data in the absence of original utilities estimates.
  
  
  METHODS
  Linear and fractional polynomial regression analyses were performed with data from a study of Parkinson's disease patients (n=138) to predict the EQ-5D index values from UPDRS and Parkinson's disease questionnaire eight dimensions (PDQ-8) data. German and European weights were used to calculate the EQ-5D index. The models were compared by R(2), the root mean square error (RMS), the Bayesian information criterion, and Pregibon's link test. Three independent data sets validated the models.
  
  
  RESULTS
  The regression analyses resulted in a single best prediction model (R(2): 0.713 and 0.684, RMS: 0.139 and 13.78 for indices with German and European weights, respectively) consisting of UPDRS subscores II, III, IVa-c as predictors. When the PDQ-8 items were utilised as independent variables, the model resulted in an R2 of 0.60 and 0.67. The independent data confirmed the prediction models.
  
  
  CONCLUSIONS
  The best results were obtained from a model consisting of UPDRS subscores II, III, IVa-c. Although a good model fit was observed, primary EQ-5D data are always preferable. Further validation of the prediction algorithm within large, independent studies is necessary prior to its generalised use.
authors.affiliation: Department of Neurology, Philipps-University, Marburg, Germany.
authors.forename: Judith
authors.initials: J
authors.lastname: Dams
authors.forename: Jens
authors.initials: J
authors.lastname: Klotsche
authors.forename: Bernhard
authors.initials: B
authors.lastname: Bornschein
authors.forename: Jens P
authors.initials: JP
authors.lastname: Reese
authors.forename: Monika
authors.initials: M
authors.lastname: Balzer-Geldsetzer
authors.forename: Yaroslav
authors.initials: Y
authors.lastname: Winter
authors.forename: Anette
authors.initials: A
authors.lastname: Schrag
authors.forename: Andrew
authors.initials: A
authors.lastname: Siderowf
authors.forename: Wolfgang H
authors.initials: WH
authors.lastname: Oertel
authors.forename: Günther
authors.initials: G
authors.lastname: Deuschl
authors.forename: Uwe
authors.initials: U
authors.lastname: Siebert
authors.forename: Richard
authors.initials: R
authors.lastname: Dodel
mesh_terms: D005260:Female; D006801:Humans; D008297:Male; D010300:Parkinson Disease / Q000175:diagnosis*; D011788:Quality of Life; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires / Q000592:standards*