title: Construct validity of the Short Form-36 Health Survey and its relationship with BMI in obese outpatients.
abstract: OBJECTIVE
  To investigate the construct validity of the Short Form-36 (SF-36) Health Survey questionnaire in obese patients.
  
  
  METHODS
  Our series consisted of 1735 obese patients (age, 44.7 +/- 11.0 years; 1346 women) consecutively enrolled in the QUOVADIS study, an observational multicenter study of obese treatment-seeking outpatients. The construct validity of the SF-36 was assessed by main component analysis. Age-, gender-, and education-adjusted general linear models were used to investigate the relationship between BMI and SF-36 domains or factors identified by main component analysis.
  
  
  RESULTS
  BMI was significantly associated with poor health-related quality of life in all eight SF-36 domains, and the strongest association was observed with physical activity. Main components analysis generated a six-factor solution explaining 59% of the observed variance. BMI was strongly associated with factors based on the loading of items regarding the physical activity domain and factors based on role-physical and role-emotional items or general health and bodily pain items. In contrast, mental health-, vitality-, and social functioning-based factors were not related to BMI.
  
  
  CONCLUSIONS
  In obese treatment-seeking outpatients, the clustering of SF-36 items in main components is not significantly different from the domain-based approach generally used, thus confirming the robustness of such a generic questionnaire in this specific condition. However, the peculiar clustering of some SF-36 items and their relationship with BMI suggest that the health-related quality of life profile of subjects belonging to that population may be better described with alternative aggregations of the SF-36 items or with disease-tailored questionnaires.
authors.affiliation: Department of Internal Medicine, University of Messina, Messina, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Corica
authors.forename: Andrea
authors.initials: A
authors.lastname: Corsonello
authors.forename: Giovanni
authors.initials: G
authors.lastname: Apolone
authors.forename: Maria
authors.initials: M
authors.lastname: Lucchetti
authors.forename: Nazario
authors.initials: N
authors.lastname: Melchionda
authors.forename: Giulio
authors.initials: G
authors.lastname: Marchesini
mesh_terms: D000328:Adult; D015992:Body Mass Index; D001835:Body Weight / Q000502:physiology; D004522:Educational Status; D005260:Female; D006306:Health Surveys; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D009765:Obesity / Q000503:physiopathology*; D010045:Outpatients / Q000706:statistics & numerical data*; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires / Q000592:standards*