title: Mapping the EORTC QLQ-C30 onto the EQ-5D-3L: assessing the external validity of existing mapping algorithms.
abstract: OBJECTIVE
  To determine the external validity of existing mapping algorithms for predicting EQ-5D-3L utility values from EORTC QLQ-C30 responses and to establish their generalizability in different types of cancer.
  
  
  METHODS
  A main analysis (pooled) sample of 3560 observations (1727 patients) and two disease severity patient samples (496 and 93 patients) with repeated observations over time from Cancer 2015 were used to validate the existing algorithms. Errors were calculated between observed and predicted EQ-5D-3L utility values using a single pooled sample and ten pooled tumour type-specific samples. Predictive accuracy was assessed using mean absolute error (MAE) and standardized root-mean-squared error (RMSE). The association between observed and predicted EQ-5D utility values and other covariates across the distribution was tested using quantile regression. Quality-adjusted life years (QALYs) were calculated using observed and predicted values to test responsiveness.
  
  
  RESULTS
  Ten 'preferred' mapping algorithms were identified. Two algorithms estimated via response mapping and ordinary least-squares regression using dummy variables performed well on number of validation criteria, including accurate prediction of the best and worst QLQ-C30 health states, predicted values within the EQ-5D tariff range, relatively small MAEs and RMSEs, and minimal differences between estimated QALYs. Comparison of predictive accuracy across ten tumour type-specific samples highlighted that algorithms are relatively insensitive to grouping by tumour type and affected more by differences in disease severity.
  
  
  CONCLUSIONS
  Two of the 'preferred' mapping algorithms suggest more accurate predictions, but limitations exist. We recommend extensive scenario analyses if mapped utilities are used in cost-utility analyses.
authors.affiliation: Centre for Health Economics, Monash Business School, Monash University, 15 Innovation Walk, Clayton, VIC, 3800, Australia. brett.doble@monash.edu.
authors.forename: Brett
authors.initials: B
authors.lastname: Doble
authors.affiliation: Centre for Health Economics, Monash Business School, Monash University, 15 Innovation Walk, Clayton, VIC, 3800, Australia.
authors.forename: Paula
authors.initials: P
authors.lastname: Lorgelly
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D003362:Cost-Benefit Analysis; D005260:Female; D006801:Humans; D016018:Least-Squares Analysis; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000523:psychology* / Q000628:therapy; D011788:Quality of Life / Q000523:psychology*; D019057:Quality-Adjusted Life Years; D011795:Surveys and Questionnaires; D055815:Young Adult
keywords: Cancer; Condition-specific non-preference-based measures; External validation; Generic preference-based measures; Mapping; Quality of life