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Re: st: Why does Stata drop an additional category?


From   Richard Williams <Richard.A.Williams.5@nd.edu>
To   statalist@hsphsun2.harvard.edu, statalist@hsphsun2.harvard.edu
Subject   Re: st: Why does Stata drop an additional category?
Date   Tue, 17 Feb 2004 10:30:42 -0500

At 09:46 AM 2/17/2004 -0500, Sarah A. Mustillo wrote:
I think I am going to have to disagree with Rich on this one and say that perhaps the additional category is being dropped because of the interaction term.
I think Sarah is correct in saying I originally got it wrong. :) But, one other thing I will note with regards to possible discrepancies between SPSS and Stata: In Stata, the command


xi: logistic unemployed  i.religion i.educ5 i.cath*e5c
results in both e5c and _IcatXe5c_1 being included in the model, even though e5c is not specified separately, i.e. Stata is including the lower order terms. But, in SPSS, a similar notation would result in only the interaction term being included and not the main effect of e5c. So, that may explain why the two programs seem to be behaving differently. So, my latest guess is that if you instead did

gen cathe5c = cath*e5c

and used that instead of i.cath*.e5c, spss and Stata would say the same things in more or less the same way. If the original questionner wants to email me his spss output I'll take a look at it. Of course, why there is both an educ5 (treated as categorical) and an ec5 (treated as continuous) is still unclear to me.

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