I. Single Tests and Series of Tests 



1. Single Tests 



All psychological experiments may be divided, ac- 

 cording to their problem, into research experiments 

 and test experiments. The latter are now generally 

 known as " tests ;" their aim is "to determine for a 

 given individual his mental constitution or person- 

 ality or to determine a single one of his mental 

 traits. 1 " Tests include, of course, not only experi- 

 ments in the narrower meaning of an investigation 

 carried out with the aid of instruments, but also 

 simple methods of procedure that do not involve the 

 use of instruments questions, problems, presenta- 

 tion of pictures, and the like provided that these 

 are administered in a systematic and scientifically 

 regulated manner and that their results are re- 

 corded. 



Now, in no field have so many tests been proposed 

 and put into operation as in the field of intelligence 

 testing. To give a complete exposition of all these 

 test methods and of the results that have been gained 

 through them would exceed the bounds of this 

 monograph. But this is not necessary, after all, be- 

 cause, as will be shown in a moment, the funda- 

 mental significance of our whole problem lies not in 



*See my earlier text (1, p. 87). 



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