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Re: st: calculating relative risk


From   Ronan Conroy <rconroy@rcsi.ie>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: calculating relative risk
Date   Wed, 5 Dec 2007 09:25:18 +0000

On 4 Dec 2007, at 22:46, Sue Kim wrote:

Hi. I have a binary outcome where the probability of
outcome is low so I want to get an adjusted relative
risk (rather than odds ratio) using glm.  When using
glm with fam(bin) link(log) command, I get a warning
"parameter estimates produce inadmissible mean
estimates in one or more observation". Could I still
use the results or is there a way to get around this
problem?
I think it's time to listen to Stata. The trouble with the relative risk is that it can produce nonsense estimates of probability in some cases. If a risk factor has a relative risk of 2, and a case has a predicted probability, based on other risk factors, of 0.6, then the addition of the final risk factor will bring the predicted risk to 1.2.

The odds ratio, for all its awkwardness, hasn't got this drawback.

Incidentally, Stata has a command -binreg- which is a canned version of what you have been doing. It has an option to give you the relative risk directly.

P Before printing, think about the environment
=================================
Ronan Conroy
rconroy@rcsi.ie
Royal College of Surgeons in Ireland
Epidemiology Department,
120 St Stephen's Green, Dublin 2, Ireland
+353 (0)1 402 2431
+353 (0)87 799 97 95
http://www.flickr.com/photos/ronanconroy/sets/72157601895416740/

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