Y
PREDICTION OF VOCATIONAL SUCCESS
(Concluded)
Prediction based on correlation. Regression line and regression equation.
Standard error of estimate. Percentile curves.
ALTHOUGH the correlation coefficient, if high, gives assurance
 that the test scores are related to success in the vocation,
 it gives no indication of the probable degree of vocational
 success of an individual who obtains a certain test
score.
To make a prediction of the unknown variable from the
known variable, the criterion from the test score, use is
made of the regression line or the regression equation. For
every correlation table there are two regression lines and
two regression equations. The one to be used depends on
which is the known variable. The investigator must always
be certain that he is using the right regression, namely, the
criterion on the test score.
Knowledge of the coefficient of correlation between test
score and criterion is not a necessary prerequisite to the use
of the regression equation, but it must be known in order to
judge the value of the regression equation.
The regression lines may be obtained in several ways. If
a scatter diagram is drawn, the mean of each column of
figures may be estimated and represented by a dot, and then
by adjusting a tight string over the diagram the straight line
may be found which best fits the dots. If this line is drawn
on the diagram, it may be used in obtaining the most probable
 value of the unknown variable, the ordinate (usually
denoted by V), corresponding to a given value of the known
variable plotted as an abscissa (X). (This is known as the

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