EMPLOYMENT PSYCHOLOGY
tion of two tests. If a scatter diagram of scores in two tests
is plotted, each individual being represented by a symbol
which indicates the class of vocational accomplishment to
which he belongs, sections of this scatter diagram may be set
off within which one grade of success is represented in rela-
tively greater proportion than the others. When these sec-
tions are mapped out, the critical scores may be stated in
terms of the two tests. For example, the statement may
take this form: “It is a favorable indication if a person
scores between % and / in Test X and at the same time scores
between mm and # in Test VV.” This method should not be
pursued unless there is ground for the belief that both tests
have differentiating value. Bills (9) has used this technique
to good effect. See Figure 26.
Several methods are open for determining the prognostic
value of answers to questions. All have as their purpose the
determination of a scoring method which will give weight to
only the significant questions in a questionnaire (or items in
a test).
If it has been found that a larger proportion of vocational
successes than of vocational failures gives a certain answer
to a question, it may be assumed that such an answer is a
favorable indication of success. We may select in any ques-
tionnaire all the questions which are answered in a certain
way by widely differing proportions of the two groups (suc-
cesses and failures), and score the questionnaire on these
items alone. Thus the individual receives a score of +1 for
each answer which is given by a larger proportion of suc-
cesses than failures; and —1 for each answer which is given
by a larger proportion of failures than successes. His score
for the questionnaire is then the algebraic sum of the scores
assigned to his significant answers.
A refinement of this procedure is to determine by formula
10 the significance of the differences in proportions, and to
include only those items where the difference in proportions
is at least twice its standard error. To be still more exact,
each answer may be assigned a weight varying with the size
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