Variation in height acceleration in the Fels growth data

The Fels growth data record at half‐yearly intervals the heights of children from birth to adulthood, and are the basis for pediatricians' growth charts used throughout North America. Aspects of human growth are the subject of a large medical and statistical literature. This paper uses smoothing splines to study the variation in height acceleration. By use of a functional version of principal‐components analysis, we find that variation in the acceleration curve is essentially three‐dimensional in nature. Evidence for a small growth spurt between the ages of six and eight, reported for data collected in Switzerland, is examined, and little support is found for the existence of this phenomenon in the Fels data.