title: Validity of self-reported height and weight and derived body mass index in middle-aged and elderly individuals in Australia.
abstract: BACKGROUND
  Body mass index (BMI) is an important measure of adiposity. While BMI derived from self-reported data generally agrees well with that derived from measured values, evidence from Australia is limited, particularly for the elderly.
  
  
  METHODS
  We compared self-reported with measured height and weight in a random sample of 608 individuals aged ≥ 45 from the 45 and Up Study, an Australian population-based cohort study. We assessed degree of agreement and correlation between measures, and calculated sensitivity and specificity to quantify BMI category misclassification.
  
  
  RESULTS
  On average, in males and females respectively, height was overestimated by 1.24 cm (95% CI: 0.75-1.72) and 0.59 cm (0.26-0.92); weight was underestimated by 1.68 kg (-1.99- -1.36) and 1.02 kg (-1.24- -0.80); and BMI based on self-reported measures was underestimated by 0.90 kg/m2 (-1.09- -0.70) and 0.60 kg/m2 (-0.75- -0.45). Underestimation increased with increasing measured BMI. There were strong correlations between self-reported and measured height, weight and BMI (r=0.95, 0.99 and 0.95, respectively, p<0.001). While there was excellent agreement between BMI categories from self-reported and measured data (kappa=0.80), obesity prevalence was underestimated. Findings did not differ substantially between middle-aged and elderly participants.
  
  
  CONCLUSIONS
  Self-reported data on height and weight quantify body size appropriately in middle-aged and elderly individuals for relative measures, such as quantiles of BMI. However, caution is necessary when reporting on absolute BMI and standard BMI categories, based on self-reported data, particularly since use of such data is likely to result in underestimation of the prevalence of obesity.
authors.affiliation: National Centre for Epidemiology and Population Health, Australian National University, Canberra, Australian Capital Territory.
authors.forename: Suan Peng
authors.initials: SP
authors.lastname: Ng
authors.forename: Rosemary
authors.initials: R
authors.lastname: Korda
authors.forename: Mark
authors.initials: M
authors.lastname: Clements
authors.forename: Isabel
authors.initials: I
authors.lastname: Latz
authors.forename: Adrian
authors.initials: A
authors.lastname: Bauman
authors.forename: Hilary
authors.initials: H
authors.lastname: Bambrick
authors.forename: Bette
authors.initials: B
authors.lastname: Liu
authors.forename: Kris
authors.initials: K
authors.lastname: Rogers
authors.forename: Nicol
authors.initials: N
authors.lastname: Herbert
authors.forename: Emily
authors.initials: E
authors.lastname: Banks
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology; D000886:Anthropometry; D001827:Body Height; D015992:Body Mass Index; D001835:Body Weight; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009517:New South Wales / Q000453:epidemiology; D009765:Obesity / Q000453:epidemiology*; D015203:Reproducibility of Results; D012650:Self Disclosure; D012680:Sensitivity and Specificity; D011795:Surveys and Questionnaires / Q000592:standards