THE RELATION BETWEEN THE GROWTH OF 
CHILDREN AND THEIR DEVIATION FROM THE 
PHYSICAL TYPE OF THEIR SEX AND AGE. 
Wma. TOWNSEND PoRTER. 
Quetelet induced from his measurements of children the 
law that the weights, heights or other physical dimensions at 
each age in the period of growth are approximations of a 
median value,’ about which they are grouped in the form of 
a probability curve, being related to the median value as the 
individual observations in a series of measurements of the 
same thing are related to its actual size. Quetelet assumed 
that the median value of an anthropometric series expressed 
the physiological type of the series and that each deviation 
from this value expressed the physiological difference between 
an individual and the type. Fifty years of research have 
placed the truth of Quetelet’s law beyond all doubt and have 
not weakened the reasonableness of his assumption, so that 
both law and hypothesis are rarely questioned and are re- 
garded as a secure base from which to explore the phenomena 
of growth. 
The degree of deviation of the individual measurements 
from the median value of an anthropometric series is meas- 
ured by the Probable Deviation, that value which, in the 
words of Lexis,” is as often exceeded as attained. Hence, if 
Quetelet’s theory is true, the Probable Deviation is a measure 
of the degree of deviation of individuals from their Physical 
Type. The Probable Deviation from the median value of a 
1 Moyenne of Quetelet, see Lettres sur la Théorie des Probabilités, Brux- 
elles, 1846, page 66; and mean of Sir John Herschel and other English writers, 
dinburg Review, 1850, page 23. 
2 Ueber die Theorie der Stabilitit statistischer Reihen. Hildebrand’s 
_ Jahrbicher fiir Nationalékonomie und Statistik. Bd. 32, 1879, S. 60-98 
