title: Validity of the SF-36 in patients with morbid obesity.
abstract: BACKGROUND
  The Medical Outcome Study 36-Item Short Form Health Survey (SF-36) is one of the most commonly applied generic quality of life instruments. The construct validity of the instrument in patients with morbid obesity is not established.
  
  
  METHODS
  A total of 475 morbidly obese patients (68% women) with a mean (standard deviation) age of 44.7 (11.8) years, weight of 123.5 (24.1) kg and BMI of 41.7 (6.3) kg/m(2), who had been referred to a rehabilitation center, completed the SF-36 form. Exploratory factor analyses were performed to examine the underlying component structure of the questionnaire. Confirmatory factor analyses were performed to assess model fit.
  
  
  RESULTS
  The analysis suggested a 6-component structure rather than the 8-component structure used in the original SF-36. The first component consisted of items from the physical functioning subscale, the role physical subscale and the general health subscale, and explained 31% of the variance. The 6 components explained 61% of the total variance. The items loaded as expected in a physical and mental component. The assessment of model fit confirmed these findings.
  
  
  CONCLUSIONS
  The 2 summary scales of the SF-36 have satisfactory validity in patients with morbid obesity. However, the validity of the 8 subscales is questionable, and the subscales should be interpreted with care.
authors.affiliation: Morbid Obesity Center, Vestfold Hospital Trust, Tønsberg, Norway. tor-ivar.karlsen@uia.no
authors.forename: Tor-Ivar
authors.initials: TI
authors.lastname: Karlsen
authors.forename: Einar K
authors.initials: EK
authors.lastname: Tveitå
authors.forename: Gerd K
authors.initials: GK
authors.lastname: Natvig
authors.forename: Serena
authors.initials: S
authors.lastname: Tonstad
authors.forename: Jøran
authors.initials: J
authors.lastname: Hjelmesæth
mesh_terms: D000203:Activities of Daily Living; D000328:Adult; D015992:Body Mass Index; D005260:Female; D006304:Health Status; D006306:Health Surveys / Q000592:standards*; D006801:Humans; D008297:Male; D008603:Mental Health; D008875:Middle Aged; D009767:Obesity, Morbid / Q000523:psychology; D011788:Quality of Life; D012017:Referral and Consultation; D012047:Rehabilitation Centers; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires / Q000592:standards*