If you estimate your model using any of the maximum likelihood methods available in PROC MIXED (METHOD=REML, ML, or MIVQUE0), then sums of squares are not available. To see how PROC MIXED forms the F-tests without sums of squares, see the Syntax: CONTRAST Statement section in the PROC MIXED documentation.

To obtain type 3 sums of squares in PROC MIXED, you can specify the METHOD=TYPE3 option in the PROC MIXED statement. This provides the expected mean squares table, in which the type 3 sums of squares are displayed. Please note that this method is used to estimate the variance-covariance parameters, but the F-tests from PROC MIXED are not computed as ratios of mean squares. They are instead computed as described in the documentation section mentioned above. Also note that the METHOD=TYPE3 option can only be specified when your model does not contain a REPEATED statement, and if you specify a RANDOM statement, then the SUBJECT= option cannot be specified.