ABSTRACT
The amount of linear correlation between two variables is expressed by a coefficient of correlation, given the symbol r . This is defined in terms of the deviations of the co-ordinates of two variables from their mean values and is given by the product-moment formula which states:
coefficient of correlation,
r = ∑
xy √{(∑
x2 )(∑
y2 )} (1)
where the x-values are the values of the deviations of coordinates X from X , their mean value and the y-values
are the values of the deviations of co-ordinates Y from Y , their mean value. That is, x =(X − X) and y =(Y −Y ). The results of this determination give values of r lying between +1 and −1, where +1 indicates perfect direct correlation, −1 indicates perfect inverse correlation and 0 indicates that no correlation exists. Between these values, the smaller the value of r , the less is the amount of correlation which exists. Generally, values of r in the ranges 0.7 to 1 and −0.7 to −1 show that a fair amount of correlation exists.
