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 assur- 
ance that the test scores are related to success in the voca- 
tion, it gives no indication of the probable degree of voca- 
tional 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 prob- 
able 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 
LVI 
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