Tools:    The table below summarizes variances of combinations of random variables.

Variance (or Square of Standard Deviation), 1 random var

                                

Variance (or Square of Standard Deviation), Any 2 rand vars

(see covariance below)

Variance (or Square of Stand Dev), 2 Independent rand vars

Covariance, any 2 random variables

Covariance, 2 Independent random variables

Correlation, any 2 random variables

Correlation, 2 Independent random variables