Minimum time intervals for serial measurements of growth in recumbent length or stature of individual children.

A method is presented to estimate minimum time intervals for meaningful measurements of growth in recumbent length or stature on individual children. These intervals are based on the statistical features of growth, and consider the reliability of measurement, expected rates of growth, and variation in attained length or stature. Because of the assumptions used, the intervals should be considered as minima, except in some predictable cases. During the prepubescent period there are no differences in minimum intervals calculated for boys and girls. The intervals are shortest during the rapid growth attending infancy, and increase to 0.39 y (4.7 mo) at 8 y of age in boys and girls, and to 0.43 y (5.2 mo) at 10 y of age in boys. A reference curve of minimum intervals for length and stature during the prepubescent period is presented with an equation for more precise estimation of measurement intervals. To accommodate the pubescent growth spurt and its normal variation in timing, 0.5 y is recommended as the minimum interval during pubescence when the maturational timing of the child is unknown. These minimum measurement intervals should be appropriate for almost all individual children when growth in recumbent length or stature is measured serially.