Since all records for trt 2 have ss=2, and all but one for trt 1 have ss=2, I would suggest rearranging the TABLES statement. If you truly need to look at the effect of ss, then put it next to last as in:
tables age*ph* trt *ss* res / riskdiff(common) alpha = 0.05 ;
Pardon the lined out part. It won't help to do anything like what I suggested there.
Because there are no records with ss=1 for any other cells in the crosstabulation, it always ends in a column associated with all zeroes for trt and res, and is excluded from riskdiff calculations. You may be able to use an EXACT statement in PROC GENMOD to include this record, but without doing a lot of digging, I don't know if that will give you what you need to calculate a riskdiff.
SteveDenham
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