INTRODUCTION 
Science finds that individuals differ, and differ widely, 
in any trait or combination of traits. They thus differ in 
their fitness for certain studies in school, games at play, 
and jobs at work. Industrial practice finds that a large 
fraction of this variability remains within a group willing 
to do a given sort of work at a given wage per hour. 
Consequently if there are ten applicants for a certain 
job there will commonly be a large advantage to the em 
ployer who selects the most fit rather than the least fit 
of the ten. Also if an individual has the choice among ten 
jobs of equal wage there will commonly be a large ad 
vantage to him if he selects the job for which he is most 
fit rather than the one for which he is least fit. Other 
things being equal, both the employer and the employee 
gain in proportion as men work at a job for which they are 
more fit than any other men are, and as each man is given 
the job for which he is better fitted than for any other 
job. The country as a whole, of course, gains very greatly 
as such a double fit is approximated. 
If sufficient ability and effort are expended it is possible 
to measure the comparative fitness of any number of men 
for any one given job, or the comparative fitness of any 
one man for any number of different jobs. These are the 
tasks of scientific personnel work, the former being the 
special work of the employment manager and the latter 
being the special work of the vocational counsellor. 
In some cases a direct trial at the job itself is still the 
best way to measure fitness; but usually the scientific 
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