HIS investigation represents a study of the beginning ages of sitting, stand-T ing and walking for a group of 349 infants reared with a relatively optimal degree of pediatric and home care. Age values in terms of central and deviational tehdencies are presented (Table I), our results are analyzed for sex differences (Tables I1 and 111), and intercorrelations of sitting, standing and walking data are determined (Table IV). Our results are compared with those of Shirley and the norms of Strang (Table V) and then our data are re-summarized by the statistic of percentage frequency values a t each age level and compared with the normative values developed by Gesell and Thompson (Table VI). And, finally, normative summaries of our results are presented a t the end.
SUBJECTS AND PROCEDUREThe source of our sample of children, and the type of pediatric care they received have been described in detail elsewhere ( 3 ) . Briefly, the 349 infants of this study lived in the Towns of Rye, New York, and Greenwich, Conn., or nearby neighborhood-an area suburban to New York City. All were in private care of the pediatrician and from homes of a t least middle class standards of living, which means that practically all of the parents of these children could afford to buy all necessary equipment and services for child care, as indicated by the pediatrician. The infants' conditions of pediatric and home care were thus relatively optimal in a t least such factors as preventive and therapeutic medicine, diet, sunshine, and exercise. Furthermore, the home environment was studied and necessary adjustments made, when possible, to insure ample rest and to prevent excessive or harmful stimulation.All observations reported on here were made by the pediatrician in the course of the routine, private care given these children. Ideally,during the first two years of development, this conformed to the following schedule of examinations, usually from one half to an hour in length, a t the pediatrician's office: infants first seen at the age of one month; then bimonthly from I to 3 months; monthly from 3 to 1 2 months; and a t least quarterly from 12 months to 2 years. However, nearly 100 of the subjects of this study were seen a t the 13th, 14th, 16th, 17th, rgth, or 20th month. Not all were seen a t each successive examination period; consequently, this study combines the cross-sectional method with the longitudinal (or sequential). Something of the population character resulting from this combined method is provided by the following summary of the 349 subjects used:(a) Of a total sample of 261 infants for whom sitting data were obtained, 156 (or 60%) were in the group of 204 infants for whom standing data were obtained, 88 AND
