The PRED_VAR output group in SURVIVAL consists of the estimate
of the predicted marginals, variance-covariance matrix for PREDMRG estimates,
Denominator degrees of freedom and Check for matrix inversion. This group
is not printed by default, though the statistics are available for individual
printing, either by explicit use of appropriate keyword(s) on the PRINT
statement or by PRED_VAR=DEFAULT or PRED_VAR=ALL on the PRINT statement.
The keywords in the PRED_VAR group are listed below in default order.