PREFACE 
Tu1s manual outlines a procedure for developing, evalu- 
ating, and installing measurement methods in vocational 
selection. It explains how to construct vocational tests and 
how to determine their reliability and validity. The con- 
struction and validation of rating scales, interest question- 
naires, application forms, interview methods, and similar 
devices used in determining aptitudes also come within its 
scope. 
So complex is the task of occupational analysis and indi- 
vidual placement, so numerous are the independent variables, 
that to some it has seemed futile to expect the ideals of 
science and the methods of measurement to be applicable. 
Others have gone to an opposite extreme, seeing in the pre- 
cision of test technique a quick relief from the uncertainties 
of personal impression. Neither of these views is justified. 
Measurement in vocational selection has gradually shown 
itself to be a feasible though slowly attainable goal. The 
techniques of experiment and statistical method have had, 
here as elsewhere, their notable triumphs. But science is 
not an easy mistress. She opens no broad highroad to suc- 
cess in selecting employees. Only a pseudo-science, ignorant 
of statistical requirements and the standards of proof, could 
pretend to teach how to read character at sight or claim 
100% accuracy in vocational selection. 
The search for genuinely scientific means of gaging abil- 
ities, demonstrably sound in principle and at the same time 
practicable, economical, useful in the routine of hiring and 
placement, is in itself a rather complicated process. This 
process of research, this adaptation of the universal prin- 
ciples of inductive logic or scientific method to the particular 
task of discovering, developing, and testing new methods of 
personnel selection, forms the subject-matter of this manual. 
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