Re: st: calculating relative risk

[Ronan Conroy <rconroy@rcsi.ie>]

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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