On the Basis of Ratio of Change Direction
a.Linear Correlation: The correlation between two variables a said to be liner if corresponding to a unit change in the values of one variable there is a constant change in the value of the other variable i ,e, in case of linear correlation the relation between the variables X and Y is of the type.
Y= a + b x
If a = 0 the relation becomes y = bx. In such cases the values of the variables are in constant ratio.
Non linear ( Curvi linear) Correlation: The correlation between two variables is said to be non linear or curvilinear in corresponding to a unit change in the value of one variable the other variable does not changes at a constant rate but at a fluctuating rate.