title: The impact of disease severity on EQ-5D and SF-6D utility discrepancies in chronic heart failure.
abstract: OBJECTIVE
  To compare EQ-5D and SF-6D utilities across groups of chronic heart failure (CHF) patients with varying levels of disease severity.
  
  
  METHODS
  A consecutive sample (N = 251) of CHF patients undergoing elective cardiac surgery were surveyed. Disease severity was proxied via a self-assessment scale, the EQ-VAS and the Duke Activity Status Index (DASI); however, validity was demonstrated only by the latter. Association and level of agreement between instruments in DASI-based severity groups were estimated with Pearson's r and the intraclass correlation coefficient (ICC), respectively. Paired-samples t test was used to identify significant differences. In a linear regression model, the DASI was used as an anchor of disease severity to identify a potential "crossover" point between EQ-5D and SF-6D utilities.
  
  
  RESULTS
  EQ-5D and SF-6D strongly correlated over the entire sample (r = 0.647, P < 0.001); however, their agreement was moderate (ICC = 0.484, P < 0.001). In the less severe DASI groups (i.e. higher functional capacity) EQ-5D was significantly higher than SF-6D (P < 0.001) and differences constituted minimally important differences (MIDs). Contrarily, in the more severe groups SF-6D was predominantly higher than EQ-5D. The regression model indicated a utility crossover point at 0.722 and predicted that individuals with a utility score less than this would score higher on the SF-6D than on the EQ-5D, and vice versa. The DASI score at crossover was calculated at 31.94.
  
  
  CONCLUSIONS
  In subgroups of patients differing in CHF severity according to the DASI, mean EQ-5D and SF-6D indices differed significantly. Contrarily, in socio-demographic and clinical groups, these utility differences were not directly evident. According to the evidence, comparisons based on severity classification via a valid disease-specific external instrument may provide insight on instrument choice in cost-utility analyses.
authors.affiliation: Faculty of Social Sciences, Hellenic Open University, Bouboulinas 57, 26222, Patras, Greece. nkontodi@otenet.gr
authors.forename: Nick
authors.initials: N
authors.lastname: Kontodimopoulos
authors.forename: Michalis
authors.initials: M
authors.lastname: Argiriou
authors.forename: Nikolaos
authors.initials: N
authors.lastname: Theakos
authors.forename: Dimitris
authors.initials: D
authors.lastname: Niakas
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002908:Chronic Disease; D005260:Female; D006115:Greece; D006305:Health Status Indicators; D006333:Heart Failure / Q000191:economics / Q000503:physiopathology* / Q000523:psychology / Q000601:surgery; D006801:Humans; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care; D011594:Psychometrics / Q000295:instrumentation; D011788:Quality of Life; D015203:Reproducibility of Results; D012647:Self-Assessment; D012720:Severity of Illness Index; D018434:Sickness Impact Profile; D012959:Socioeconomic Factors; D011795:Surveys and Questionnaires / Q000592:standards*
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