Now that we have the relevant sums and sums of squares for our raw data (see chart below), we can continue with our sums of squares calculations for the various effects in the design.

We calculate an estimate of the grand mean that is used in many formulas, calculate an estimate for the total sums of squares, and then calculate a sums of squares estimate for each effect in the design -- main effect for Factor A (Severity of Crime), main effect for Factor B (Time of Testing) and the interaction of Factor A and Factor B (Severity x Time). Finally, we calculate the sums of squares estimate for the within-group variance, which serves as our error term.