This question is perhaps a bit weird. I've run the same do-file on the same .dta file multiple times, and the results vary. I thought I would go crazy and my perception of reality was almost shattered, since there is no instruction related to random numbers. But before jumping out of the window, I realized that there is a gen var = mod function that could be causing problems. I have done some research and it has not gone well, therefore I go to this forum to see if you can give me some background on this problem. Thank you and sorry for my poor English.