Validity of parentally reported versus measured weight, length and waist in 7- to 9-year-old children for use in follow-up studies

The aim of this prospective cohort study was to assess the validity of parentally reported anthropometric data compared to measured data in 7- to 9-year-old Flemish children especially for use in follow-up studies. The subjects were 116 Flemish children of a birth cohort recruited in the first Flemish Environment and Health Study (2002-2003). Data about anthropometric measures (waist circumference (WC), weight and length) were obtained by a postal parentally reported questionnaire and during a home visit. Our study showed that parents tend to overreport their child's WC and underreport the BMI, especially in children with large WC and high BMI. The median difference between measured and parentally reported WC was 1.6 % of the median measured WC; for BMI, the median difference was 2.8 % of the median measured BMI. Both for WC and BMI, we observed a good agreement between parentally reported values and measured values to classify children in the highest 10 and 20 % of the study population. When classifying the children in 'overweight' and 'not overweight', there were less misclassifications when parentally reported WC was used compared to parentally reported BMI. Conclusions: Although there is a high agreement between parentally reported and measured WC, the parentally reported data must be used with reserve. Moreover, this study is the first to suggest that WC is a better indicator compared to BMI when parentally reported values are used to classify children.