Hello everyone,

unfortunately, I can't tell you which Stata-Version I was using, since I used a remote access client to work on a server. I can't access the server anymore, I only have the results and some of the code available.

I have a dataset with patients in different regions and I am looking at differences in the probability of being referred to a specialist by regions. For each patient I have a dummy variable, indicating whether she is referred (referral), a categorical variable indicating the region (region) and several control variables. I first used a logit regression and then predicted the probability with the margins command.

Code:
logit referral i.region controlvars, robust

margins region
My base category is region 1 in the output. Region 2 has a coefficient of 0.598, which results in an odds ratio of e(0.598) = 1.818. However, when I look at the results of the margins command, the average adjusted prediction that is calculated with the magins command gives a probability of 0.775 for region 1 and a probability of 0.823 for region two. Calculating the odds ratio with these probabilities gives a completely different results: (0.823/(1-0.823) / (0.775/(1-0.775)) = 1.349. Does anyone know why these differences arise? Is there a logical explanation for that which I can give when showing my results, or did I mistake somewhere in my calculation?

Best regards,
Nina König