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MEMOIRS NATIONAL ACADEMY OF SCIENCES. 



[Vol. XV, 



The selection of tests for the abbreviated scale was based upon the following considera- 

 tions: (1) Diagnostic value; (2) order of difficulty; and (3) necessity of retaining tests which 

 would give mental ages as nearly as possible identical with those based on the entire scale. 



The diagnostic value of the tests for white soldiers is roughly indicated by rapidity of 

 increase in the per cents passing at various mental ages. Table 65, which shows this for the 

 various tests, presents interesting comparisons. Some tests show a very gradual, others a very 

 rapid increase in number passing with mental age. Obviously, the more gradual the increase 

 the more tests must be used to secure a reliable measure. It will also be noted that there is 

 usually some particular mental level where a test shows the most rapid rise in number passing, 

 above this level the increase being so slight that the diagnostic value of the test for this class of 

 subjects becomes greatly reduced. Table 65 includes the total number of cases (486). All 

 tests below those • actually given a subject were considered to have been passed; those above 

 the point where the examination ended, to have been failed. In comparing the figures of this 

 table it should be borne in mind that below mental age 7 and above mental age 18 the numbers 

 are much too small to be significant. 



i 

 Table 65. — Per cent passing each Stanford-Binet test at each mental age (ivhite recruits). 



Table 66 shows the order of difficulty of the tests based upon the number of men failing in 

 each. The number passing and the number doubtful are also shown. It should be noted that 

 the order of difficulty for soldiers differs considerably from that for school children; compre- 

 hension and making change, for example, are relatively much easier for adults, while the test 

 of reversed digits is much harder for adults than for children of the same mental age. 



