Validity of self-reported weight and height in Austrian adults: sociodemographic determinants and consequences for the classification of BMI categories

Objective: Epidemiological studies have shown that adults tend to underestimate their weight and overestimate their height. This may lead to a misclassification of their BMI in studies based on self-reported data. The aim of the present study was to assess the validity of self-reported weight and height in Austrian adults. Design: Data on weight, height, health behaviour and sociodemographic characteristics of adults were collected in a standardized procedure via a self-filling questionnaire and a medical examination including measurements of weight and height. Setting: A publicly accessible out-patient clinic in southern Austria. Subjects: Austrian residents (n473) aged 18 years and older who attended a health check participated in the study. Results: The mean difference between reported and measured BMI was not significant in younger adults (<35 years: mean difference -0.21 kg/m(2); P < 0.08) but increased significantly with age (>= 55 years: mean difference -0.68 kg/m(2); P<0.001). The prevalence of normal weight (BMI = 18.5-24.9 kg/m(2)) and overweight (BMI = 25.0-29.9 kg/m(2)) was overestimated based,on the self-reported data on BMI, while that for underweight (BMI < 18.5 kg/m(2)) and obesity (BMI >= 30.0 kg/m(2)) was underestimated (P < 0.001). The self-reported data showed an obesity prevalence of 12.5%, while measurement showed a prevalence of 15.4% (P < 0.001). Conclusions: Our results indicate that prevalence rates of obesity are probably underestimated for Austrian adults when using self-reported weight and height information. The deviations from the measured data clearly increased with age. Analyses based on self-reported data should therefore be adjusted for the age dependency of the validity.