I have the following proc reg statement, but for some reason, it gives me the "No variables specified for an SSCP matrix. Execution terminating." Here is my proc reg statemen: proc reg data = simdata_no_violations noprint outest = MyEst_no_violations;   by sim; run; I was wondering if it was my by statement, but I'm not sure.  The sim variable is just the number of simulated dataset.  And at the moment, I have 5 simulated datasets from the dataset. Does anybody know why that warning occurs? Thanks!, , ... View more