\(r = \frac{\displaystyle\sum_{i=1}^{n} (x_i - \bar{x})(y_i - \bar{y})} {\sqrt{\displaystyle\sum_{i=1}^{n} (x_i - \bar{x})^2} \sqrt{\displaystyle\sum_{i=1}^{n} (y_i - \bar{y})^2}}\)