DISTRIBUTION OF COLLEGE CREDITS 399 



The curve for these facts was printed and sent to each instructor with an 

 explanation of its meaning, and a superimposed red curve showing in 

 each case precisely how the instructor's distribution differed from the 

 norm. A table was prepared showing the distribution of grades for all 

 courses having 80 or more students. 3 The range for each grade in per- 



E C A^^ 



Mean and Extreme Distributions 

 of Grades A~E 



Total Grades = 27S7 Mean Distribution = Extreme Distributions = 



centages was as follows: 



A 0.7-20 



B 6-39 



C 27-62 



D 0-31 



E 0-20 



Accordingly, we have scientific grounds for assuming that a theo- 

 retically correct distribution of the grades of college students will ap- 

 proach the normal surface of frequency (Fig. 9, A and B) unless the 

 group is subject to selection. In that case the curve would be skewed 

 negatively or positively as in Fig. 10. 



3 In Bulletin 368 of the University of Wisconsin, Professor Dearborn at- 

 tempts to justify the normal distribution of grades " from the fact that it is 

 used in actual practise." Two objections may be made to this contention: 

 first, very few instructors do closely approximate the normal distribution; 

 second, as their practises have no scientific basis, any one of them could only 

 by accident indicate the theoretically correct distribution. If, however, all of 

 Professor Dearborn's curves were . represented by one, made from thousands of 

 grades by scores of instructors, it would conform more closely to the general 

 biological law of variation than any of the curves he presents. 



