THE METHOD OF AGE GRADATION 



43 





(a) General distribution of the level of intelli- 

 gence. In those investigations where there have 

 been tested a large number of elementary school 

 pupils of different ages and with no attempt at spe- 

 cial selection, there could be worked out general sta- 

 tistics of the number of children that are at, above 

 or below the mental level of their age. I bring to- 

 gether in the following table the percentages thus 

 far obtained. 



TABLE I. 



DISTRIBUTION OF THE LEVEL OF INTELLIGENCE FOR ALL AGES 

 COLLECTIVELY. 



3 Children from 5 to 10 years old. 

 4 Children from 5 to 11 years old. 

 Includes two or more years below or above age. 



Binet (37, p. 112) has brought together a frequency distribution 

 of 203 normal children (ages not given). In this distribution we 

 may note a remarkable symmetry : almost exactly one-half of the 

 children are 'at age,' a good quarter are 'below age,' and a scant 

 quarter are 'above age.' 



Bobertag has called attention to this peculiarly simple sym- 

 metrical numerical distribution that he had noted first in his own 

 results and then found confirmed in Binet. 



Bobertag has just published his own frequency distribution. I 

 take from it (40, II, Table I) the figures for 261 children between 

 5 and 10 years. While here, again, the 'at age' children comprise 

 half of all the cases, the divergence between the two other groups 

 is but slight the 'advanced' are somewhat more numerous than 

 the 'retarded' children. 



A third set of data, derived from a much more extensive ma- 

 terial, has been given us by Goddard (48), who has tested all the 

 school children of a small American city (Vineland, N. J.). The 

 distribution curve that Goddard has prepared from his raw figures 



