With the classification of a point pair into an angle/distance class, as shown earlier in this section, the semivariance computation proceeds as follows.

Denote all pairs that belong to angle class and distance class as . For example, based on Figure 98.20 and Figure 98.21, belongs to .

Let denote the *number* of such pairs. The component of the standard (or method of moments) semivariance that correspond to angle/distance class is given by

where is the average distance in class ; that is,

The robust version of the semivariance is given by

where

This robust version of the semivariance is computed when you specify the ROBUST option in the COMPUTE statement in PROC VARIOGRAM.

PROC VARIOGRAM computes and writes to the OUTVAR= data set the quantities , and .