title: Comparison of the EQ-5D and the SF-6D utility measures in 813 patients with early arthritis: results from the ESPOIR cohort.
abstract: OBJECTIVE
  The revolution of early aggressive therapy in early arthritis (EA) has fueled the search for better approaches to establish cost-effectiveness. Our objective was to compare the EuroQol EQ-5D health outcome measure and the SF-6D and to investigate their relationship to clinical variables in a large prospective cohort of patients with EA.
  
  
  METHODS
  The EQ-5D and SF-6D utility measures were longitudinally assessed in 813 patients with EA. Agreement and aspects of validity (construct validity, discrimination) were assessed.
  
  
  RESULTS
  At baseline, mean values for EQ-5D were 0.52 ± 0.31 (range -0.59 to 1.0) and for SF-6D were 0.58 ± 0.11 (range 0.30 to 0.92), with a bimodal distribution for the EQ-5D. Agreement was low for patients with severe disability or active disease: the utility was systematically lower with EQ-5D. The intraclass correlation coefficient was 0.42 at baseline and increased to 0.53 at 6 months and 0.57 at 1 and 2 years. Correlations between the 2 utility scores and the Health Assessment Questionnaire were good, and remained similar and stable over 2 years (r = -0.70). Correlations with the Disease Activity Score for 28 joints and the physical component of the MOS 36-item Short-form Health Survey (SF-36) were moderate to good and stable. In contrast, correlation with the mental component of the SF-36 was better with the SF-6D, and the correlation with pain, weak at baseline, improved at 6 months and remained stable thereafter. The SF-6D was better able to discriminate patients with high disease activity.
  
  
  CONCLUSIONS
  There was systematic disagreement between EQ-5D and SF-6D in EA, especially in patients with worse clinical outcomes. Using the 2 instruments could be appropriate to conduct sensitivity analyses of cost-utility ratios because the instruments measure utility with closely similar measured properties, but at different levels.
authors.affiliation: INSERM, CIC-EC CIE6, Nancy, France. cecilegaujouxviala@yahoo.fr
authors.forename: Cécile
authors.initials: C
authors.lastname: Gaujoux-Viala
authors.forename: Anne-Christine
authors.initials: AC
authors.lastname: Rat
authors.forename: Francis
authors.initials: F
authors.lastname: Guillemin
authors.forename: René-Marc
authors.initials: RM
authors.lastname: Flipo
authors.forename: Patrice
authors.initials: P
authors.lastname: Fardellone
authors.forename: Pierre
authors.initials: P
authors.lastname: Bourgeois
authors.forename: Bruno
authors.initials: B
authors.lastname: Fautrel
mesh_terms: D000328:Adult; D001168:Arthritis / Q000191:economics / Q000503:physiopathology*; D015331:Cohort Studies; D003362:Cost-Benefit Analysis; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D008137:Longitudinal Studies; D008875:Middle Aged; D017063:Outcome Assessment, Health Care; D011594:Psychometrics / Q000295:instrumentation*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D011795:Surveys and Questionnaires / Q000592:standards*