Covarianceฯxy=E[XY]โE[X]E[Y]\sigma_xy = \mathbb{E}[XY] - \mathbb{E}[X] \mathbb{E}[Y]ฯxโy=E[XY]โE[X]E[Y] where E[XY]\mathbb{E}[XY]E[XY] is the correlation.ฯxy=ฯxyฯxฯy\rho_{xy} = {\sigma_{xy} \over {\sigma_x \sigma_y}}ฯxyโ=ฯxโฯyโฯxyโโ โ1โคฯxyโค1-1 \leq \rho_{xy} \leq 1โ1โคฯxyโโค1