: EMPLOYMENT PSYCHOLOGY
highly with the tests. It is not necessary for the tests to
predict exactly what a man’s standing in the measure of
vocational accomplishment will be; it is only necessary to
know whether the tests predict accurately whether he will
be a success or a failure. If the measure of vocational success
 is continuous, it remains to find where the division line
shall be placed for success and failure in order to obtain the
highest correlation with the tests. By calculating biserial 7
with the numbers in the alternative categories varying (that
is, by calling the successes the upper 10%, 20%, or 30% in
the criterion of success), the division point may be found
which yields the highest correlation with the test, and the
criterion of success may then be fixed at that point. On the
other hand, the alternative categories may be set with regard
to test scores, the criterion being continuous, and the optimum
 critical score obtained by finding the dividing line the
use of which yields the highest correlation with the criterion.
The results will be in terms of “per cents” and will have to
be transmuted into scores. This method of determining
critical scores has little advantage over the method of inspection.

Ruml (160, p. 59) gives elsewhere the formula for the
rank-tangential coefficient (¢) which is equivalent to biserial
7 applied to ranked data.
The correlation ratio (7) is a truer measure than 7 of the
relationship between two variables if this relationship is
curvilinear. The formula is
em) a
(23) pm Ve
where 7. is the number of measures in a column, ¥. the arithmetic
 mean of the column, ¥ the arithmetic mean of all the
’s in the table, o, the standard deviation of all the ¥’s in
the table, and NV the total number of measures. The correlation
 ratio is greater than the correlation coefficient where the
regression is non-rectilinear, but in rectilinear regression the

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