Fitting a Null Model
In some situations you may want to fit a null model. For instance,
by fitting a null model, you can trick PROC PHREG into providing the
Kaplan-Meier estimate of the
survivor function for a set
of survival times with right censoring and left truncation.
In the following SAS program, t2 is the survival time,
t1 is the left truncation time, and c is the censoring
indicator with value 1 indicating censored observations. By not
specifying
any explanatory variables in the MDOEL statement, you are fitting a null
model. The sdf variable in the output data set out1 contains
the product-limit estimates.
proc phreg;
model t2*c(1)= /entrytime=t1 ;
output out=out1 survival= sdf;
run;
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