141 EMPLOYMENT PSYCHOLOGY
formance; of a rating scale, an expression of opinion; and
of a questionnaire, a statement of fact.
In an investigation of the sort we are describing, the main
purpose of the questionnaire is to gather information for
validation regarding the individual’s personal and family
history, his health and habits, and those elements of his
social environment, interests, tastes, motives, and personality,
 for the measurement of which tests or rating scales
are not adaptable. Much of this material will be available
to the investigator on the regular application blanks of the
company, but a thorough study usually demands that information
 be obtained in greater detail, and with a broader
selection of questions.
The questionnaires used in research will differ only in
length from the ones later used in actual selection of employees.
 They must be made to include all possibly significant
 items, or a sufficiently large number of items. It is
too much to expect that more than a minor fraction of these
items will show a significant correlation with the criterion of
success. The number of items should, therefore, be large
enough to allow for this shrinkage and still leave an abundance
 of valid items to include in the employment questionnaires
 developed as a result of this investigation.
The same point holds with reference to the number of
sources from which information is sought. The research
questionnaires may be devised for filling out by the applicant
 or employee himself, by the interviewer, by the employee’s
 references, by fellow-workers or supervisors, by the
medical examiner, and by an investigator who obtains the
data from company records or other sources.
When the material has been validated and the questionnaires
 condensed to include only significant questions, the
information can be obtained for employment purposes from
more limited sources: From the applicant himself at the
interview, from the applicant’s references, and from the

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