THE METHOD OF AGE GRADATION 69 



number of the children (83 in all) that he had tested 

 in 1909. The reapplication of the same tests does 

 not seem to have caused any noticeable difficulty, be- 

 cause the memory of the details of the testing of the 

 year before had as good as entirely disappeared. 

 This experiment throws light upon three problems. 

 In the first place it sheds an unexpectedly favorable 

 light upon the reliability of the test method. Bober- 

 tag arranged the 83 children in order on the basis of 

 the number of tests solved by each of them and 

 found that the order in the two years coincided very 

 closely, in fact the correlation amounted to 0.95. 

 Accordingly, even if the absolute grading into the 

 different age-levels of intelligence that the Binet- 

 Simon method affords is still somewhat uncertain, 

 yet it is demonstrably very certain in its relative 

 gradings. The position that a child takes in a group 

 of children on the basis of a single testing of his in- 

 telligence may be deemed to possess a high degree 

 of reliability. 



In the second place there comes to light a clear 

 relation between the mental status of a child and the 

 rate of his subsequent intellectual development. 

 Those children that ranked 'at age' in the first test- 

 ing had advanced next year exactly one year, on the 

 average, while the retarded children had advanced 

 only two-thirds of a year, and the advanced children 

 one year and a quarter in the same period. 



In the third place Bobertag found that the num- 

 ber of children that deviated, either above or below 

 the level of their age, increased as their age in- 

 creased. It follows from this that, as chronological 

 age increases, the gradation of ages becomes pro- 



