42 PSYCHOLOGICAL METHODS OP TESTING INTELLIGENCE 



when children of approximately equal age-levels are 

 under investigation can this value suffice: for all 

 other cases the introduction of the mental quotient 

 will be recommended farther on (cf. pp. 80 ff.). This 

 value expresses not the difference, but the ratio of 

 mental to chronological age and is thus partially in- 

 dependent of the absolute magnitude of chronological 

 age. The formula is, then : mental quotient = mental 

 age -r- chronological age. With children who are just 

 at their normal level, the value is 1, with those who 

 are advanced, the value is greater than unity, with 

 those mentally retarded, a proper fraction. The 

 more pronounced the feeble-mindedness, the smaller 

 the value of the fraction. 



Another and last concept that * mental age' sup- 

 plies is that of mental arrest. This applies only to 

 feeble-minded individuals and means a mental age 

 that is not exceeded, despite increase of chronolog- 

 ical age. 



3. Results with Normal Children 



The investigation of normal children forms a pre- 

 condition of the whole method, since the norm for 

 each age must first be determined upon them. Yet, 

 at the same time, investigations of these children 

 have already brought out a series of results that 

 permit us to set no slight value on the future worth 

 of intelligence tests for the problems of normal peda- 

 gogy. Thus far, tests have been made chiefly upon 

 children in the common schools of both sexes and 

 of different ages, less often upon pupils of the higher 

 schools. 



