628 



MEMOIRS NATIONAL ACADEMY OF SCIENCES. 



[Vol. XV, 



any item correctly responded to counts whether or not preceding items have elicited incorrect 

 responses. Thus those individuals who reach the last item in a test, but who find there more 

 than ordinary difficulty, are massed in the next lower class interval, although many may have 

 had time to have done items on the average even more difficult had they been available. Thus 



the histogram of beta test 7 is accounted for. 



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Beta test 1 shows a distribution very much skewed but giving no clear indication of the 

 limitation of range displayed by many other tests. Beta 2 is similarly negatively skewed and 

 also somewhat limited at the lower end of its range. Beta 3 defies interpretation. 



