Development of a pediatric body mass index using longitudinal single-index models.

As a measure of human adiposity, the body mass index, defined as weight/height(2), has been widely used in clinical investigations. For children undergoing pubertal development, whether this function of height and weight represents an optimal way of quantifying body mass for assessing of specific health outcomes has not been carefully studied. In this study, we propose an alternative pediatric body mass measure for prediction of blood pressure based on recorded height and weight data using single-index modeling techniques. Specifically, we present a general form of partially linear single-index mixed effect models for the determination of this new metric. A methodological contribution of this research is the development of an efficient algorithm for the fitting of a general class of partially linear single-index models in longitudinal data situations. The proposed model and related model fitting algorithm are easily implementable in most computational platforms. Simulation demonstrates superior performance of the new method, as compared to the standard body mass index measure. Using the proposed method, we explore an alternative body mass measure for the prediction of blood pressure in children. The method is potentially useful for the construction of other indices for specific investigations.