title: The relationship between EQ-5D, HAQ and pain in patients with rheumatoid arthritis.
abstract: OBJECTIVE
  This study aims to provide robust estimates of EQ-5D as a function of the HAQ and pain in patients with RA.
  
  
  METHODS
  Repeated observations were made of patients diagnosed with RA in a US observational cohort (n = 100 398 observations) who provided data on HAQ, pain on a visual analogue scale and the EQ-5D questionnaire. We used a bespoke statistical method based on mixture modelling to appropriately reflect the characteristics of the EQ-5D instrument and to compare this with results from standard multiple regression.
  
  
  RESULTS
  EQ-5D can be predicted from summary HAQ and pain scores. We identify four different classes of respondents who differ in terms of disease severity. Unlike the multiple regression, the mixture model exhibits very good fit to the data and does not suffer from problems of bias or predict values outside the feasible range.
  
  
  CONCLUSIONS
  It is appropriate to model the relationship between HAQ and EQ-5D but only if suitable statistical methods are applied. Linear models underestimate the quality-adjusted life year benefits, and therefore the cost-effectiveness, of therapies. The bespoke mixture model approach outlined here overcomes this problem. The addition of pain as an explanatory variable greatly improves the estimates. Reimbursement agencies rely on these types of analyses when formulating policy on the use of new drug therapies. Clinicians as well as economists should be concerned with these issues.
authors: Health Economics and Decision Science, School of Health and Related Research, University of Sheffield, Sheffield S1 4DA, UK.
authors: Mónica
authors: M
authors: Hernández Alava
authors: Allan
authors: A
authors: Wailoo
authors: Fred
authors: F
authors: Wolfe
authors: Kaleb
authors: K
authors: Michaud
mesh_terms: D000328:Adult; D000368:Aged; D001172:Arthritis, Rheumatoid / Q000175:diagnosis* / Q000628:therapy*; D015331:Cohort Studies; D004185:Disability Evaluation; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D010147:Pain Measurement / Q000379:methods*; D011788:Quality of Life; D019057:Quality-Adjusted Life Years; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires; D016896:Treatment Outcome; D006113:United Kingdom