title: Validity, responsiveness, and minimal important difference for the SF-6D health utility scale in a spinal cord injured population.
abstract: OBJECTIVE
  To determine the feasibility, acceptability, discriminative validity, responsiveness, and minimal important difference (MID) of the SF-6D for people with spinal cord injury (SCI).
  
  
  METHODS
  A total of 305 people with SCI completed the SF-36 health status questionnaire at baseline and at subsequent occurrence of a urinary tract infection (UTI) or 6-month follow-up. Normative SF-36 data were obtained from the Australian Bureau of Statistics. SF-36 scores were transformed to SF-6D utility values using Brazier's algorithm. We used UTI as the external criterion of clinically important change to determine responsiveness and two categories of the SF-36 transition question ("somewhat worse" and "somewhat better") as the external criterion to determine the MID. Derived SF-12 responsiveness was also assessed.
  
  
  RESULTS
  The mean SF-6D values were: 0.68 (SD 0.21, n = 305) all patients; 0.66 (SD 0.19, n = 167) tetraplegia; 0.72 (SD 0.26, n = 138) paraplegia; 0.57 (SD 0.15, n = 138) with UTI. The Australian normative SF-6D mean value was 0.80 (SD 0.14, n = 18,005). The SF-6D was able to discriminate between SCI and the Australian normative sample (effect size [ES] = 0.86), tetraplegia-paraplegia (ES = 0.23), and it was responsive to UTI (ES = 0.86 SF-36 variant, ES = 0.92 SF-12 variant). The MID for respondents who reported being somewhat worse or somewhat better at follow-up was 0.03 (SD 0.17, n = 108/305), while the MID for only those who were somewhat worse was 0.10 (SD 0.14, n = 58).
  
  
  CONCLUSIONS
  The content of the SF-6D is more appropriate than that of the SF-36 for this physically impaired population. The SF-6D has discriminative power and is responsive to clinically important change because of UTI. The MID is consistent with published estimates for other disease groups.
authors.affiliation: Prince of Wales Spinal Unit, Prince of Wales Hospital, Sydney, NSW, Australia. blee@medicalinformatics.net
authors.forename: Bonsan Bonne
authors.initials: BB
authors.lastname: Lee
authors.forename: Madeleine T
authors.initials: MT
authors.lastname: King
authors.forename: Judy M
authors.initials: JM
authors.lastname: Simpson
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Haran
authors.forename: Martin R
authors.initials: MR
authors.lastname: Stockler
authors.forename: Obaydullah
authors.initials: O
authors.lastname: Marial
authors.forename: Glenn
authors.initials: G
authors.lastname: Salkeld
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D003430:Cross-Sectional Studies; D016002:Discriminant Analysis; D005240:Feasibility Studies; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D008297:Male; D008875:Middle Aged; D009517:New South Wales; D011594:Psychometrics / Q000295:instrumentation*; D011788:Quality of Life; D015203:Reproducibility of Results; D013119:Spinal Cord Injuries / Q000150:complications* / Q000523:psychology*; D011795:Surveys and Questionnaires; D014552:Urinary Tract Infections / Q000209:etiology* / Q000523:psychology*