I'm building a predictive model for a medical condition that happens in both men and women. Physicians have reported that in some cases for women, their menstrual history seems to be a risk factor, though epidemiologists haven't been able to verify this claim. My data includes information about female subjects' menstrual history. My goal is to build a logistic regression model that determines the probability of the existence of this condition. Here's my problem: I'd like to build a model that includes gender and includes menstrual history questions for female subjects, but how do I assign values for male subjects for things like "number of months since last pregnancy"? Is there a general method to deal with this kind of problem?