title: The validity of self-reported body mass index in a population-based osteoarthritis study.
abstract: BACKGROUND
  Obesity is a well-known risk factor for osteoarthritis (OA). The majority of obesity research in OA is performed using self-reported BMI-data, however, its validity in persons with OA is unknown. The aim of this study was to compare the validity of self-reported body mass index (BMI) in persons with and without clinical osteoarthritis (OA) in a population-based survey.
  
  
  METHODS
  Height and weight were self-reported, and thereafter measured in 600 persons with and without clinical OA according to the American College of Rheumatology-criteria (knees, hips and/or hands). We compared the differences between measured and self-reported heights, weights and BMIs (kg/m2) for the two groups and explored whether demographic/clinical factors were associated with inaccurate reporting in the OA patients using multivariate linear regression analyses.
  
  
  RESULTS
  Mean (SD) age was 64 (8.7) years and 412 (69%) were women. Participants with clinical OA (n = 449) underreported their BMI to a greater extent than participants without clinical OA (n = 151) [mean (SD) difference 1.34 (1.68) kg/m2 and 0.78 (1.40) kg/m2 (p = 0.000), respectively]. There was a strong dose-dependent association between higher measured BMI and greater underreporting of BMI in multivariate analyses (BMI 25-29.99 kg/m2: B = 0.40, 95% CI, 0.06, 0.77), BMI ≥ 30 kg/m2: B = 1.30, 95% CI, 0.86, 1.75) in the clinical OA patients. A higher age as well as the time interval from self-reported to measured BMI-data were associated with inaccurate reporting.
  
  
  CONCLUSIONS
  Researchers using self-reported height and weight data should be aware of limited agreement with actual height and weight in overweight and obese individuals with clinical OA.
authors.affiliation: National Advisory Unit on Rehabilitation in Rheumatology, Department of Rheumatology, Diakonhjemmet Hospital, Post box 23, Vinderen, 0319 Oslo, Norway. magnusson_karin@hotmail.com.
authors.forename: Karin
authors.initials: K
authors.lastname: Magnusson
authors.forename: Ida K
authors.initials: IK
authors.lastname: Haugen
authors.forename: Nina
authors.initials: N
authors.lastname: Østerås
authors.forename: Lars
authors.initials: L
authors.lastname: Nordsletten
authors.forename: Bård
authors.initials: B
authors.lastname: Natvig
authors.forename: Kåre Birger
authors.initials: KB
authors.lastname: Hagen
mesh_terms: D000328:Adult; D000368:Aged; D015992:Body Mass Index; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010003:Osteoarthritis / Q000175:diagnosis* / Q000453:epidemiology*; D011159:Population Surveillance / Q000379:methods; D015203:Reproducibility of Results; D057566:Self Report / Q000592:standards*