After a group of tests has been given and each test has been 
rated, the result is a collection of ratings which is often very 
confusing. It is quite necessary, from every point of view, to 
be able to express all these ratings in terms of a single rating 
for the entire group. This is sometimes done by adding to 
gether the results in each test, a procedure which is obviously 
fallacious, because each test may have a different value. 
The value of each test is determined by its index of correla 
tion. The tests for inspectors, for instance, were found to have 
correlations of plus .56 for 2, plus .63 for 6, and plus .72 for 8. 
Therefore, test 8 should be given more weight in the final result 
than 6, etc. The proportional value of each test may be approxi 
mately found by dividing each correlation by the sum of all the 
correlations. In the above instance this gives .30 for 2, .32 for 
6, and .38 for 8. That is, test 2 is to count 30% of the total, 
test 6, 32%, and test 8, 38%, no matter what the record in 
each test is. 
Pro-rating is the process of applying a formula by which the 
rating in a group of tests can be combined in such a way as to 
give each rating its proportional value in the final result. If 
we use the results of the above analysis, and apply it to the 
inspectors’ test, we shall have the following formula: 
.30 X 2r + .32 X 6r + .38 X 8r = R, in which R is the final 
group rating, and 2r, 6r, and 8r the rating in each of the three 
tests. If our deduction has been correct, R should be 1.00 
when each test has been done in reference time. E. g., .30 X 1.00 
+ .32 X 1.00 + .38 X 1.00 = 1.00. 
It is impossible to apply this formula to any ratings which 
are not computed on a standard basis similar to that described 
under the section on rating. 
It is also desirable to pro-rate tests in accordance with chang 
ing and special conditions. For instance, in the case of clerical 
tests, it may be necessary to place considerable emphasis on 
the arithmetical test, especially for ledger, statistical, and ac