Hi all, I have a question about interaction when using proc logistic for data analysis.   I have a binary outcome death(0/1) and two binary predictors, MIHP(0/1) and black(0/1).  I ran the following codes.  To fit a logistic model with interaction between MIHP and black, I do go with two ways as follows.  I expect to see exactly the same results in the output of the two ways, but I do not.  Can anyone explain why? Way#1: adding MIHP|black to the right hand side of the model statement Way#2: first creating interaction variablein interact=MIHP*black, then adding MIHP, black, and interact to the rightside of the model statement The two ways provide excatly the same model fit statistics (AIC, SC, and -2LogL), but the MLE of the parameters are not the same. Why this happens? Which is the correct one? Or they should be used differently? Thanks for the help, Zhiying ... View more