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I am doing a binary logistic regression analysis. I got one categorical predictor with 7 levels. When I try to do this in Minitab 17 I get an error message: "The model could not be fit. Maximum likelihood estimates of parameters may not exist due to quasi-complete separation of data points." If I exclude 5 of the levels and only test the two I am actually interested in, I do not get this message. But I guess that simply excluding levels does not come without a cost and would need to be corrected for? (Even if these two, control vs special treatment, were the ones I was interested in.)
Does anyone know of a way out of this (other than adding more data since I do not have that option)? In R maybe? Or another test?