In Reply.—Dr Walravens' letter suggests the use of Z scores instead of percentiles in calculating growth rates in infants with caloric-deprivation failure to thrive. There are many standards that can be used in calculating growth velocity. Dr Walravens' method is valid and should yield rates of growth as accurate as the rates described in our study.
We chose percentiles as our standards of comparison because they are readily available in the most commonly used pediatric textbooks, and therefore it is more likely that the calculation of the growth rate will be performed by the practicing physician with this method. Most pediatricians have a copy of the Nelson Textbook of Pediatrics1; few, if any, have the PCTL9D Anthropometry Subroutine. Using Z scores, as Dr Walravens suggests, will produce useful results; but, by recommending percentiles, a standard with which most physicians are familiar and to which they have easy access,
ELLERSTEIN NS, OSTROV BE. Growth Quotients, Z Scores, and Failure to Thrive-Reply. Am J Dis Child. 1985;139(9):862. doi:10.1001/archpedi.1985.02140110016016