I have a question:
I would like to test the proportional assumption for our data.
At first, I used,
proc phreg data = pfsdays;
class trt;
model ept*eptcen(1) = trt / rl;
assess var = (trt) ph;
run;
I got : ERROR: Cannot assess the functional form of ATRSORT since it is not
a continuous explanatory variable.
Then I created a numeric var, trtpn, 0, 1 correspoding to two treatment
groups. No error.
The code I used is:
ods graphics on;
proc phreg data = pfsdays;
model ept*eptcen(1) = trtpn / rl;
assess var = (trtpn) ph;
run;
ods graphics off;
I got two plots for the assess statemetns, Cumulative Martingale function form,
and Standardized Score Process Plot.
I cannot copy the plot here. Sorry.
Before day 300, the plot is above 0, fluctuated lot, then after 300, it is still above 0, but almost flat.
My question is: since my trtpn only has two values, 0, 1, so I use it in the
assess statement is correct, or wrong? If it is correct, how to explain the
results? If it is not correct, how to use the “assess” statement to
test the ph assumption?
Thanks any one!!