94 PSYCHOLOGICAL METHODS OF TESTING INTELLIGENCE 



The fitness of a test to be employed at all, and its 

 assignment to a given age-level is something that we 

 shall be able in the future to work out by different 

 methods. 



In the first place we have to make use of the rela- 

 tion between the age-level and the test. In general, 

 for a test to be valid for a certain level, the require- 

 ment is that approximately 75 per cent, of all chil- 

 dren of this age shall be able to pass the test. This 

 requirement would correspond to the normal stand- 

 ard of validity previously mentioned (p. 45 f.), and 

 Bobertag, as more recently Bell (32), has actually 

 checked up the assignment of given tests to given 

 age-levels in accordance with this principle ; Terman 

 and Childs (63) take 66 per cent, for the critical 

 value, though this would seem, for the reasons al- 

 ready cited, to be less appropriate. 



Taken alone, however, this principle is inadequate, 

 for it does not inform us whether the test would be 

 characteristic for just this age-level only and not 

 just as much or nearly as much for another age-level. 

 To determine this we must discover with what fre- 

 quency the test is passed in other ages; and that 

 test is most useful that shows the most decided ad- 

 vance with age (a helpful methodological device to 

 which Bobertag was the first to call attention). 



For the sake of illustration let us invent an example. Suppose 

 two tests have each been passed successfully by 75 per cent, of 

 9-year-old children, but that the one test shows little, the other 

 decided difference in the frequency with which it is passed by 

 8- and 10-year old children. If Test A be passed by 65, 75 ami 80 

 per cent, of 8-, 9- and 10-year old children, respectively, and Test B 

 by 45, 75 and 90 per cent, in the same three ages, respectively, then 

 the latter test sets a task whose performance is just normal for 

 the 9-year-old, as compared with the 8-year-old children, and prac- 

 tically a self-evident activity for 10-year-old children; Test B is 

 then the more useful test 



