THE METHOD OF AGE GRADATION 77 



of feeble-minded children lags progressively more 

 and more behind their chronological age : the 

 younger they are, the more, and the older they are, 

 the less does a year's retardation mean in actual de- 

 f ectiveness. ' ' 



How considerable the fluctuations are may be 

 shown by some figures (Table X) that I have de- 

 rived from one of Chotzen's tables (p. 485). In ad- 

 dition to the tests, or rather independently of them, 

 Chotzen examined all the pupils of the special school 

 as the physician and the psychiatrist ordinarily 

 would, and classified them, on the basis of this ex- 

 amination, into the stock groups moron, imbecile, 

 idiot. Some he had to class outside of these groups 

 by designating them as 'not feeble-minded' or as 

 ' doubtful feeble-minded.' Now, it might be sup- 

 posed that the members of any group, e. g., the 

 morons, would necessarily show at least approxi- 

 mately the same degree of mental endowment, re- 

 gardless of differences in their chronological ages. 

 But Table X shows that their mental retardation, 

 computed as the absolute difference, has very dif- 

 ferent values with the older than with the younger 

 children, and Table XI, in which the average value 

 of this measure of retardation has been figured for 

 each age-level, reveals a rapid increase in the mag- 

 nitude of the value, so that the 12-year-old imbeciles 

 are retarded by twice as many years as the 8-year- 

 old imbeciles (4.7 as against 2.3 years). 



From this it seems to me to follow that the abso- 

 lute difference can be used only when we are dealing 

 with children of a given age. If, for example, it 

 should sometime be arranged to carry out tests of 



