An analogue to covariance for three variables. For three variables x, y, and z with values xi, yi, zi, i=1,…,n, the comvariance is com(x,y,z) = Si=1…n(xi-m(x))(yi-m(y))(zi-m(z)), where m(·) is the mean of the values in its argument. Due to Deardorff (1982).