Validity of Self-reported Height, Weight, and Body Mass Index of the Korea Youth Risk Behavior Web-based Survey Questionnaire

Background: Self-reported anthropometric values such as height and weight are used to calculate body mass index (BMI) and assess the prevalence of obesity among adolescents. The aim of this study was to evaluate the validity of self-reported height, weight, and BMI of the Korea Youth Risk Behavior Web-based Survey questionnaire.

Methods: A convenience sample of 137 middle and 242 high school students completed a self-administered web-based questionnaire in 2008. Body height and weight were directly measured after self-reported values were obtained from the questionnaire survey. Differences between self-reported and measured means for height, weight, and BMI were assessed by subtracting the measured values from the self-reported values. Sensitivity, specificity, and kappa statistics were computed in order to evaluate the validity of the prevalence of obesity (BMI ≥95 percentiles or ≥25 kg/m²).

Results: Self-reported weight and BMI tended to be underestimated. Meanwhile, self-reported height tended to be overestimated, except for middle school boys. The prevalence estimate of obesity based on self-reported data (10.6%) was lower than that based on directly measured data (15.3%). The estimated sensitivity of obesity based on self-reported data was 100% and the specificity was 94.7%. The value of kappa was 0.79 (95% confidence interval, 0.70-0.88).

Conclusion: This study demonstrated that self-reported data led to the underestimation of BMI and consequently the prevalence of obesity. Direct measurements of height and weight need to be performed for the accurate assessment of obesity among adolescents.