EMPLOYMENT PSYCHOLOGY
angles. He must show, first, that the selective method he
has devised has greater predictive accuracy than the methods
 hitherto used in forecasting the vocational success of
applicants. He must show, second, that when consideration
is given both to cost of installation and operation of the
selection methods and to increase in efficiency of operating
departments resulting from selection of workers with higher
vocational accomplishment, use of the new method will result
 in a net economic saving.
RELATIVE PREDICTIVE ACCURACY
The methods of selection most commonly used in industry
are of two sorts. They depend either on general impressions
gained from application blank and personal interview or on
the use of one of the many pseudoscientific methods of character
 analysis. In either case it devolves upon the investigator
 to make an evaluation of the accuracy of prediction by
these methods, employing the same rigorous procedure as in
the evaluation of his own examinations, and using the same
criterion of vocational accomplishment. Only under these
conditions can a real comparison be made.
If the interview is emphasized in the method of selection
in use, the judgments of independent interviewers may be
compared. In most instances the wide disagreement among
interviewers will provide an opportunity for demonstrating
the greater objectivity of tests.
Wembridge (218) compared the validity of an intelligence
test modeled upon Army Alpha and Beta with interviewers’
judgments of probable success. His subjects were several
hundred machine operators in a clothing plant. The method
of payment was that of piece rates with bonuses for a certain
standard of quantity and quality. This standard was determined
 by time studies and was applicable to all workers.
The criterion of success was the percentage of this standard
attained by the worker. The criterion and ratings by two

216