A modified locally weighted method for developing reference standards for height, weight, and body mass index of boys and girls aged 4 to 18 in Taiwan

The objectives of this study are to modify the locally weighted method to obtain reference values for height, weight, and body mass indices (BMI); to describe the median growth velocity of children aged 4 to 18 in Taiwan; and to compare those values with data from other countries. We modified the LOCAL method to generate empirical percentiles and used the locally weighed regression to smooth the percentiles. We examined the smoothed percentiles against original data to ensure that smoothed percentiles were within 1% of errors. We used numerical differentiation of the 50th percentiles of height and weight to obtain the velocity of growth in height and weight, respectively. We applied our method to the data of the Nutrition and Health Survey in Taiwan, 1993-1996, which was a multistaged stratified sample. The sample included 2351 boys and 2355 girls aged 4 to 18. Our results indicate that (a) the proposed method, which utilizes the original data, guarantees the percentiles within 1% errors; (b) before puberty, the height, weight, and BMI of Taiwanese children are not much different from those of their counterparts in Western countries; and (c) after puberty and at the stage of young adulthood, the height, weight, and BMI of Taiwanese youth are below the levels of those in Western young adults. Genetic makeup and dietary patterns may contribute to these phenomena.