AGE-RELATED REFERENCE RANGES FOR GROWTH-PARAMETERS

We propose an approach to the computation of age-related reference ran ges which guarantees that the proportion of sampled data points covere d by the reference band has an arbitrarily specified value. Unlike oth er approaches in the literature, this method does not have to rely on parametric distributional assumptions. The boundaries of the bands are given by smooth curves, and for modeling the mean as a function of ag e, a sufficiently flexible class of monotonically increasing functions is used, since in the applications all measured variables are biologi cal growth parameters. The width of the reference band is allowed to b e proportional to any suitably fixed function of age which we propose in practice to be taken linear. The approach is illustrated by example s from a large-scale study of the distribution of fetal size measureme nts obtained by routine prenatal sonography.