Validity, responsiveness, and minimal important difference for the SF-6D health utility scale in a spinal cord injured population.
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.
Lee
Bonsan Bonne
BB
Prince of Wales Spinal Unit, Prince of Wales Hospital, Sydney, NSW, Australia. blee@medicalinformatics.net
King
Madeleine T
MT
Simpson
Judy M
JM
Haran
Mark J
MJ
Stockler
Martin R
MR
Marial
Obaydullah
O
Salkeld
Glenn
G
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*