THE METHOD OP AGE GRADATION 103 



confronts them with a different attitude. 28 But if we 

 had at our disposal other equivalent series of tests, it 

 would be possible to make repeated testings of the 

 same individuals more frequently. In the same way, 

 when group tests were carried on, those children 

 between whom there might be danger of collusion 

 could be tested with different series. Finally, it is 

 valuable to have a supplementary series at hand in 

 case an investigation is rendered worthless by dis- 

 turbance or ineptitude of any sort. 



When we shall have undertaken simply those try- 

 outs of a considerable number of single tests sug- 

 gested above (cf. pp. 92 ff.), we shall certainly have 

 enough at our command to arrange parallel series 

 for each year : though there will be some difficulty in 

 securing an approximate equivalence between the 

 corresponding scales. 



There has been some demand for yet another kind 

 of extension of the scale. As it has appeared that 

 the mental differences are extreme between one year 

 and another in the case of the younger children, the 

 need has been felt of intermediate stages, as for in- 

 stance for specific standards for such age-levels as 

 6.5, 7.5 and 8.5 years. In our opinion this need is 

 to be satisfied in another way, viz., by use of the 

 mental quotient, since this permits us to take frac- 



28 Binet had five 9-year-old children tested twice with the same 

 tests with a 14-day interval. On the average, the children passed 

 2.5 tests more on the second trial an amount that would signify 

 an increase of a half-year in mental age (pp. 164-5). As Bobertag 

 has shown, the danger resident in repetition is not so great as this 

 when the interval is longer (see above, p. 69) ; yet even under 

 these conditions the use of the same tests is but a make-shift and 

 a second and a third repetition of the same tests would be surely 

 quite out of the question. 



