The correlation is the calculation of the relationship between two or more variables.

A correlation is said to be perfect if all the values of the variables exactly correspond to an equation (for example, there is a perfect correlation between the side of a square and its area), whereas a partial correlation is said to exist when this condition is not met.

Correlation Index, measures the degree of correlation between two variables. the correlation index can assume values in the range [-1 ; +1].

If the correlation index = -1 the correlation is perfect negative

If the correlation index = +1 the correlation is perfect positive