title: Comparison of Use of Short Form-36 Domain Scores and Patient Responses for Derivation of Preference-Based SF6D Index to Calculate Quality-Adjusted Life Years in Patients with Intermittent Claudication.
abstract: BACKGROUND
  The short form 36 (SF36) questionnaire is used for assessment of generic quality of life. Responses to the individual question in SF36 are also used for calculation of the SF6D index score. This score is used for calculation of quality adjusted-life years (QALYs) in economical analyses. As the individual patient questionnaires are not always available for performing systematic reviews and meta-analyses, a new formula has been developed for derivation of SF6D index score from the reported SF36-domain scores. This study aimed to evaluate the validity of this formula for use in patients with intermittent claudication.
  
  
  METHODS
  A retrospective review of a prospectively collected database of a randomized controlled trial was performed. A total of 178 patients were recruited. Clinical indicators of ischemia were recorded. All patients completed SF36 questionnaires. Response and domain-based SF6D scores (R-SF6D and D-SF6D) and QALYs were calculated. Correlation and agreement analysis were performed.
  
  
  RESULTS
  Response rate was 88% (n = 781) over a 1-year follow-up period. Domain-based SF6D score (mean, 0.684; standard deviation [SD] 0.110) was significantly higher (paired t-test, P = 0.001) than the response-based score (mean, 0.627; SD, 0.110) with a mean difference of 0.056 (95% confidence interval, 0.053-0.060). Mean QALY calculated using D-SF6D score (0.503; SD, 0.116) was also significantly higher than the QALY calculated from the R-SF6D score (0.467; SD, 0.121). Bland-Altman comparison showed strong agreement (limit of agreement -0.167 to 0.054) between the 2 methods with equal variances (Pitman's test, P = 0.629). D-SF6D scores showed stronger correlation with clinical indicators of ischemia (r = 0.246-0.602) compared with that of R-SF6D scores (r = 0.233-0.549).
  
  
  CONCLUSIONS
  Domain-based estimation of SF6D score is a valid and reliable method with strong agreement to the gold standard response-based scores in claudicants. However, adjustments may be required in studies using a mixture of D-SF6D and R-SF6D scores for QALY calculation.
authors.affiliation: Academic Vascular Surgical Unit, Vascular Department, University of Hull, Hull, UK. Electronic address: fayyaz.mazari@nhs.net.
authors.forename: Fayyaz Ali Khan
authors.initials: FA
authors.lastname: Mazari
authors.affiliation: Academic Vascular Surgical Unit, Vascular Department, University of Hull, Hull, UK.
authors.forename: Yousef
authors.initials: Y
authors.lastname: Shahin
authors.affiliation: Academic Vascular Surgical Unit, Vascular Department, University of Hull, Hull, UK.
authors.forename: Junaid Alam
authors.initials: JA
authors.lastname: Khan
authors.affiliation: Academic Vascular Surgical Unit, Vascular Department, University of Hull, Hull, UK.
authors.forename: Nehemiah
authors.initials: N
authors.lastname: Samuel
authors.affiliation: Academic Vascular Surgical Unit, Vascular Department, University of Hull, Hull, UK.
authors.forename: Daniel
authors.initials: D
authors.lastname: Carradice
authors.affiliation: Academic Vascular Surgical Unit, Vascular Department, University of Hull, Hull, UK.
authors.forename: Peter Thomas
authors.initials: PT
authors.lastname: McCollum
authors.affiliation: Academic Vascular Surgical Unit, Vascular Department, University of Hull, Hull, UK.
authors.forename: Ian Clifford
authors.initials: IC
authors.lastname: Chetter
mesh_terms: D000368:Aged; D016208:Databases, Factual; D005260:Female; D006801:Humans; D007383:Intermittent Claudication / Q000175:diagnosis* / Q000191:economics / Q000503:physiopathology / Q000523:psychology; D008297:Male; D008875:Middle Aged; D057240:Patient Preference; D011237:Predictive Value of Tests; D011788:Quality of Life; D019057:Quality-Adjusted Life Years; D016032:Randomized Controlled Trials as Topic; D015203:Reproducibility of Results; D012189:Retrospective Studies; D011795:Surveys and Questionnaires; D013997:Time Factors