Linear Correlation Coefficient

The correlation coefficient is a statistical measure that indicates how a change in the value of one variable affects the other.
When the value of a variable changes in the same direction as the other, we say that there is a positive correlation or positive correlation coefficient. On the contrary the correlation is negative. However, when a variable increases or decreases in value, at random, the correlation is null or does not exist.
In the Cartesian system where the independent variables are on the axis (x) and the dependent variables on Y axis, the correlation is linear when the points are distributed in the straight line. When the points spread around a curve, we say that the correlation is not linear.
In so far as, the independent variables deviate from the straight line, the correlation is perfect, moderate or imperfect.
The correlation coefficient ranges from -1 to +1 and the closer to the ends, more strong, the correlation.
Thus, we have the interpretations:
0.9           more or less, very strong correlation;
0.7 to 0.9 positive or negative, strong correlation;
0.5 to 0.7 positive or negative, moderate correlation;
0.3 to 0.5 positive or negative, weak correlation;
0 to 0.3   positive or negative, negligible correlation;
A good example for correlation: Total sales and commercial visitors.
How to calculate Linear Correlation Coefficient.

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