CHAPTER IX. 
THE APPLICATION TO INDIVIDUAL SCHOOL CHILDREN OF THE MEAN VALUES 
DERIVED FROM ANTHROPOLOGICAL MEASUREMENTS BY THE GENERALIZING 
METHOD. 
The data for the studies described in this work can be col- 
lected either by the ‘< generalizing ’’ or by the ‘ individualiz- 
ing’’ plan. In the former, a great number of measurements 
is made but once on individuals of different ages, and the 
measurements classified according to age. In the latter, the 
same individuals are measured yearly or oftener during their 
period of growth, and the measurements classified also by 
age. The generalizing method, the one pursued in the present 
investigation, is rapidly and easily carried out, whereas the 
individualizing method demands for its execution exceptional 
opportunities and exceptional patience, requiring not only 
that the measurements be made and the records kept through 
two decades, but that the number of children measured in the 
early years of this long period be very great, lest death and 
desertion so thin the ranks that those remaining to the end 
shall be too few to yield trustworthy conclusions. Both 
methods, when applied to the same material, give identical 
results with regard to means, including those of subdivisions 
as well as those of the whole number of observations. The 
individualizing method does more. 
The importance of the individualizing method has been much 
emphasized, for the reason that it can give information without 
which the laws derived from means cannot, in the present state 
of knowledge, be applied to individuals. Before this appli- 
cation can be made, it is necessary to know the degree of prob- 
ability that an individual, who at a given age stands at a certain 
deviation from the mean of any dimension will show the same 
deviation at other ages; for example, the degree of probability 
that a girl whose height at age 8 is 122.06 cm., and who 
therefore deviates 3.7 em., or +1d from the mean of her age 
(118.36 cm.), will deviate to the same degree (+1d) from 
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