title: Effect of the type of population on estimates of mean body mass index and prevalence of overweight and obesity: a systematic review of studies of Portuguese adults.
abstract: BACKGROUND
  Prevalence estimates for overweight/obesity vary widely between studies, reflecting true differences across settings and biased sampling.
  
  
  OBJECTIVE
  To compare mean body mass index (BMI) and prevalences of overweight/obesity in samples of different types of population, in Portugal.
  
  
  METHODS
  A systematic review was conducted to identify studies that assessed the distribution of BMI and overweight/obesity in different populations (general population, blood donors, university students, occupational groups, healthcare users and volunteers). Linear regression was used to quantify age-, sex- and survey year-adjusted differences in these outcomes.
  
  
  RESULTS
  When weight/height were measured, BMI was higher among blood donors (+1.4 kg/m(2)) and lower in occupational groups ( - 0.9 kg/m(2)), compared to the general population. Overweight prevalence was lower among university students ( - 5.2%). Obesity prevalence was higher among occupational groups (+4.5%) and healthcare users (+8.9%); and lower in volunteers ( - 6.4%). With self-reported data, BMI was lower among university students ( - 0.9 kg/m(2)), occupational groups ( - 1.2 kg/m(2)) and volunteers ( - 0.7 kg/m(2)). Healthcare users had higher overweight (+6.7%) and lower obesity prevalences ( - 4.3%) and occupational groups lower obesity prevalence ( - 5.7%).
  
  
  CONCLUSIONS
  Estimates varied largely across population types. Commonly used solutions for an easier assembling of study samples are likely to yield biased estimates of the distributions in the general population.
authors.affiliation: Department of Clinical Epidemiology, Predictive Medicine and Public Health, University of Porto Medical School, Porto, Portugal. hcarreira@med.up.pt
authors.forename: Helena
authors.initials: H
authors.lastname: Carreira
authors.forename: Marta
authors.initials: M
authors.lastname: Pereira
authors.forename: Ana
authors.initials: A
authors.lastname: Azevedo
authors.forename: Nuno
authors.initials: N
authors.lastname: Lunet
mesh_terms: D000328:Adult; D015992:Body Mass Index; D016001:Confidence Intervals; D006801:Humans; D009765:Obesity / Q000453:epidemiology* / Q000503:physiopathology*; D011157:Population Dynamics; D011174:Portugal / Q000453:epidemiology; D015995:Prevalence