EMPLOYMENT PSYCHOLOGY 
psychologists to devise tests for definite abilities. It does 
not enable the investigator to separate the wheat from the 
chaff in his series of tests. It leaves room for grave doubts 
whether the tests are responsible for any improvement that 
is observed. Correct scientific procedure requires that each 
test be validated separately on individual workmen of 
known vocational efficiency. Group criteria become sec- 
ondary and may be used later to demonstrate to the manage- 
ment the economic savings effected by use of the tests. 
The choice of a criterion of occupational success will 
vary with the use to which it is to be put as well as with 
the extent and dependability of available records. Mea- 
sures of output are by all odds the best criterion if the 
worker’s output is conditioned mainly by his own ability 
and persistence, and not by factors outside of his control. 
Time required to learn the job is a good criterion where 
training is expensive. Length of service, as expressed in 
terms of ability and willingness to hold down the job for 
at least six months (or some other suitable period) is a 
clear-cut criterion of success which has proved extremely 
useful in selection studies. In jobs where high proficiency is 
essential, the worker’s measured performance in a well- 
standardized trade test or searching proficiency examina- 
tion is the best gage of his actual ability. Ratings or super- 
visor’s estimates of relative success are, on the other hand, 
the least dependable of criteria, to which recourse will be 
had reluctantly, and only when the management cannot 
provide a more reliable and objective measure of occupa- 
tional accomplishment. 
When the criterion or criteria have been selected and 
have been approved by the executive most interested in the 
installation of the tests, the next step is the selection, on 
the basis of these vocational criteria, of men to serve as 
subjects for the investigation. 
48