title: Does disease activity add to functional disability in estimation of utility for rheumatoid arthritis patients on biologic treatment?
abstract: OBJECTIVE
  Treatment in general is mostly directly aimed at disease activity, and measures such as the DAS28 might therefore present important additional information. Our aim was to develop and validate a model that uses a combination of disease activity (DAS28) and HAQs to estimate EuroQoL 5-dimension scale (EQ5D) utilities.
  
  
  METHODS
  Longitudinal data from a cohort study in RA patients from the Utrecht Rheumatoid Arthritis Cohort study Group (Stichting Reumaonderzoek Utrecht) who started treatment with a biologic drug were used for mapping and validation. All 702 observations, including DAS28, HAQ and EQ5D assessed at the same time points, were used. The observations were randomly divided into a subset for development of the model (n = 428 observations) and a subset for validation (n = 274). A stepwise multivariable regression analysis was used to test the association of DAS28 (components) and HAQ (domains) with EQ5D. Model performance was assessed using the explained variance (R(2)) and root mean square errors. Observed and predicted utility scores were compared to check for under- or overestimation of the scores. Finally, the performance of the model was compared with published mapping models.
  
  
  RESULTS
  Lower DAS28 score and HAQ items dressing and grooming, arising, eating, walking and activities were associated with higher EQ5D scores. The final model had an explained variance of 0.35 and a lower root mean square error as compared with other models tested. The agreement between predicted and observed scores was fair.
  
  
  CONCLUSIONS
  HAQ components estimate EQ5D better than total HAQ. Adding DAS28 to HAQ components does not result in better utility estimations.
authors: Department of Rheumatology and Clinical Immunology, University Medical Centre Utrecht, S.C.Nair@umcutrecht.nl.
authors: Sandhya C
authors: SC
authors: Nair
authors: Department of Rheumatology and Clinical Immunology, University Medical Centre Utrecht.
authors: Paco M J
authors: PM
authors: Welsing
authors: Department of Rheumatology and Clinical Immunology, University Medical Centre Utrecht.
authors: Anne Karien C A
authors: AK
authors: Marijnissen
authors: Diakonessenhuis Utrecht.
authors: Paulina
authors: P
authors: Sijtsma
authors: Department of Rheumatology and Clinical Immunology, University Medical Centre Utrecht.
authors: Johannes W J
authors: JW
authors: Bijlsma
authors: Department of Rheumatology and Clinical Immunology, University Medical Centre Utrecht.
authors: Jacob M
authors: JM
authors: van Laar
authors: Department of Rheumatology and Clinical Immunology, University Medical Centre Utrecht.
authors: Floris P J G
authors: FP
authors: Lafeber
authors: Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht and National Institute of Public Health and the Environment, Bilthoven, The Netherlands.
authors: G Ardine
authors: GA
authors: de Wit
mesh_terms: D000203:Activities of Daily Living; D001172:Arthritis, Rheumatoid / Q000188:drug therapy / Q000503:physiopathology / Q000534:rehabilitation*; D001688:Biological Products / Q000627:therapeutic use*; D004185:Disability Evaluation; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology*; D011379:Prognosis; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires
chemical_list: D001688:Biological Products
keywords: DAS28; EQ5D; HAQ; QALY; biologics; functional limitation; mapping; prediction; rheumatoid arthritis; utility