Bill,

There was a fairly long discussion of this issue on the Stata listserv. As
far as I could tell, the short answer is that the RRR is not the same as the
OR, because the coefficients from a logistic regression are not the same
(they are a special case) as the coefficients from a multinomial logit
(however if you run a multinomial logit on a binary dependent variable
OR=RRR).  But you can follow the thread for yourself from here:

http://www.stata.com/statalist/archive/2005-06/msg00063.html

Omar.


----- Original Message -----
From: "William Ford, University of Chicago" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, May 04, 2006 8:22 PM
Subject: [POLMETH] Stata: mlogit & RRRs


>I hope someone might be able to clear up what should be a
> simple question, though I cannot find the simple answer.
>
> Stata's mlogit command reports logit coefficients by default.
> By using the RRR option, Stata will supposedly report relative
> risk ratios instead. But Stata's method of generating these
> "relative risk ratios" is simply to exponentiate the
> coefficients. Stata says, "rrr reports the estimated
> coefficients transformed to relative risk ratios, i.e., exp(b)
> rather than b."
>
> But exponentiating the coefficients is how one converts logit
> coefficients to odds ratios. Since odds ratios and relative
> risk ratios are not the same thing (though in some cases they
> may be almost equal), Stata’s description of these
> exponentiated coefficients as relative risk ratios makes no
> sense to me. Shouldn’t Stata just call these numbers odds
> ratios? And shouldn't I just call them odds ratios too?
>
> Thanks for any guidance.
>
> Bill
>
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