84 PSYCHOLOGICAL METHODS OF TESTING INTELLIGENCE 



tioned, so that for many problems it can be neglected. 

 Before and after these ages the fall in the value 

 seems to take place more rapidly. In the case of the 

 later age-levels this is easily intelligible, for once 

 the stage of arrest that we have previously dis- 

 cussed is reached (for morons at the mental age of 

 9), the quotient obtained by dividing mental by 

 chronological age must decrease as chronological 

 age increases. The feeble-minded child, it must be 

 remembered, not only has a slower rate of develop- 

 ment than the normal child, but also reaches a stage 

 of arrest at an age when the normal child's intelli- 

 gence is still pushing forward in its development. 

 At this time, then, the cleft between the two will be 

 markedly widened. 



From these considerations it follows that the 

 mental quotient can hold good as an index of feeble- 

 mindedness only during that period when the de- 

 velopment of the feeble-minded individual is still in 

 progress. It is for this reason that there is no sense 

 in calculating the quotient for idiots, because, in 

 their case, the stage of arrested development has 

 been entered upon long before the ages at which 

 they are being subjected to examination. The above- 

 mentioned gradual tendency of the mental quotient 

 to sink during the progress of development shows 

 that this development approaches the final level of 

 arrest at a progressively decreasing rate. 22 



Whether we shall succeed some time in finding a 

 formula for a truely constant coefficient of feeble- 

 mindedness must be left for the future. 



^In his last article (40, II) Bobertag lays special stress on this 

 progressive retardation in the rate of development of the feeble- 

 minded and attempts to present it in graphic form. 



