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TEE POPULAR SCIENCE MONTHLY 



dents, is a good example. In all cases the distribution closely approxi- 

 mates the normal type. 



Does the distribution of the complex abilities that determine excel- 

 lence in college courses approximate this normal type? Theoretically 

 it should, and our theory is supported in a striking way by the distri- 

 bution of 8,969 grades in twenty-one elementary courses for two years, 

 1907-08, at Harvard College. The curve in Fig. 11, representing this 

 distribution, is nearly normal. The percentages for the grades A-E 

 are, respectively, 7, 20, 42, 21, 7. Yet there are wide variations among 



90-100 



the instructors in these very courses. In fact not a single instructor 

 came as near to a normal distribution as the sum of all their grades. 

 Now, no one of these markers is as likely to tell the truth as all to- 

 gether. Their several errors correct each other and thus give us, in 

 Fig. 11 (Group 1), a close approximation to the type of curve we 

 should expect to have with an infinite number of cases. In 1909-10, 

 the grades in certain elementary courses in Harvard College (Chem- 

 istry 1, Comparative Literature 1, English A, Government 1, History 1, 

 Mathematics F, Philosophy C, Zoology 1) were distributed in the fol- 

 lowing percentages: A = 5.5, B = 21, C = 44, D = 19.5, E = 9. 



