Anthropological Measurements of Children. 23 



OX THE APPLICATION TO INDIVIDUAL SCHOOL CIIIL 



DRP:N OF THE MEAN VALUES DERIVED FROM 



ANTHROPOLOGICAL MEASUREMENTS BY 



THE GENERALIZING METHOD. 



By W. Towxsend Porter, M.D., 

 Assistant Pkofessor of Physiology ix the Harvard Medical School. 



I. 



Tlie method employed by Quetelet in liis anthroponietrical 

 studies of the phenomena of human growtli was based on two 

 fundamental propositions, (1) the mean of a great number of 

 individuals of the same class is the typus or norm of the 

 class; and (2) the deviations of individuals from the typus 

 follow the law of accidental causes, and are subject to the 

 calculus of probabilities. 



From these propositions it results that the typus in any 

 dimension, e. ^., height, at any age in the period of growth, is 

 the mean of a sufficient!}' large number of observations of 

 that dimension at the given age, and that the degree with 

 which the observed approaches the true mean can be deter- 

 mined by an application of the principle of least squares. 



When the means of any one dimension, for example, height 

 at each age in the period of growth, are compared, the law 

 of growth in that dimension is at once apparent, and may be 

 expressed graphically in a curve whose abscissae are years, and 

 whose ordinates are centimetres, kilogrammes, or other units 

 of measurement. Not only is the mean at any age thus fixed, 

 but the probability of any given deviation from that mean is 

 fixed as well. Thus the mean height of 2192 St. Louis Public 

 School girls,* aged 8, is 118.36 cm., with a probable error of 



* W. Townseiid Porter, "The Physical Basis of Precocity and Dullness," Transactions 

 of the Academy of Science of St. Louis, Vol. VI, Xo. 7, March 21, 1893, pp. 161 -181. Also 

 " Untersucliungen der Schulkinder in Bezug auf die physischen Grundlagen ihrer geisti- 

 gen Entwickelung," read before the Berliner Gesellschaft fur Anthropologic, Ethnologic, 

 und Urgeschichte, July 15, 1893, and published in Virchow's Ztitschrift fur Ethnologie. 



