title: Can Mapping Algorithms Based on Raw Scores Overestimate QALYs Gained by Treatment? A Comparison of Mappings Between the Roland-Morris Disability Questionnaire and the EQ-5D-3L Based on Raw and Differenced Score Data.
abstract: BACKGROUND
  Mapping algorithms are increasingly being used to predict health-utility values based on responses or scores from non-preference-based measures, thereby informing economic evaluations.
  
  
  OBJECTIVE
  We explored whether predictions in the EuroQol 5-dimension 3-level instrument (EQ-5D-3L) health-utility gains from mapping algorithms might differ if estimated using differenced versus raw scores, using the Roland-Morris Disability Questionnaire (RMQ), a widely used health status measure for low back pain, as an example.
  
  
  METHODS
  We estimated algorithms mapping within-person changes in RMQ scores to changes in EQ-5D-3L health utilities using data from two clinical trials with repeated observations. We also used logistic regression models to estimate response mapping algorithms from these data to predict within-person changes in responses to each EQ-5D-3L dimension from changes in RMQ scores. Predicted health-utility gains from these mappings were compared with predictions based on raw RMQ data.
  
  
  RESULTS
  Using differenced scores reduced the predicted health-utility gain from a unit decrease in RMQ score from 0.037 (standard error [SE] 0.001) to 0.020 (SE 0.002). Analysis of response mapping data suggests that the use of differenced data reduces the predicted impact of reducing RMQ scores across EQ-5D-3L dimensions and that patients can experience health-utility gains on the EQ-5D-3L 'usual activity' dimension independent from improvements captured by the RMQ.
  
  
  CONCLUSIONS
  Mappings based on raw RMQ data overestimate the EQ-5D-3L health utility gains from interventions that reduce RMQ scores. Where possible, mapping algorithms should reflect within-person changes in health outcome and be estimated from datasets containing repeated observations if they are to be used to estimate incremental health-utility gains.
authors.affiliation: Warwick Clinical Trials Unit, Division of Health Sciences, Warwick Medical School, University of Warwick, Coventry, CV4 7AL, UK. j.j.madan@warwick.ac.uk.
authors.forename: Jason
authors.identifier: http://orcid.org/0000-0003-4316-1480
authors.initials: J
authors.lastname: Madan
authors.affiliation: Warwick Clinical Trials Unit, Division of Health Sciences, Warwick Medical School, University of Warwick, Coventry, CV4 7AL, UK.
authors.forename: Kamran A
authors.initials: KA
authors.lastname: Khan
authors.affiliation: Warwick Clinical Trials Unit, Division of Health Sciences, Warwick Medical School, University of Warwick, Coventry, CV4 7AL, UK.
authors.forename: Stavros
authors.initials: S
authors.lastname: Petrou
authors.affiliation: Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, Medical Science Division, University of Oxford, Oxford, OX3 7HE, UK.
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Lamb
mesh_terms: D000328:Adult; D000465:Algorithms; D005260:Female; D006304:Health Status; D006801:Humans; D017116:Low Back Pain / Q000175:diagnosis* / Q000191:economics / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D011788:Quality of Life; D019057:Quality-Adjusted Life Years; D011795:Surveys and Questionnaires