[R] Relative Risk in logistic regression

[John Sorkin]

If you use a log link, you are not, I believe, performing a logistic regression!

 
John David Sorkin M.D., Ph.D.
Chief, Biostatistics and Informatics
University of Maryland School of Medicine Division of Gerontology
Baltimore VA Medical Center
10 North Greene Street
GRECC (BT/18/GR)
Baltimore, MD 21201-1524
(Phone) 410-605-7119
(Fax) 410-605-7913 (Please call phone number above prior to faxing)>>> "Kevin E. Thorpe" <kevin.thorpe at utoronto.ca> 1/30/2013 11:22 AM >>>
On 01/30/2013 11:17 AM, John Sorkin wrote:
> I am not sure why one would want a relative risk from a logistic
> regression. The measure of association from a logistic regression is the
> odds ratio, not the relative risk.
> John
>

Yes, the natural measure, when using the logit link, is the OR.  I 
always use that myself, but if you use the log link, you get RR.  As for 
why you would, I would suggest it's because physicians think they 
understand a RR better than and OR.


> "Kevin E. Thorpe" <kevin.thorpe at utoronto.ca> 1/30/2013 11:14 AM >>>
> On 01/30/2013 09:02 AM, nalluri pratap wrote:
>  > Relative risk = exp(coef(model))
>  >
>
> Only if you fit using the log link.  Using the logit link, this gives
> odds ratios.
>
>  > --- On Wed, 30/1/13, aminreza Aamini <amin.r.fan at gmail.com> wrote:
>  >
>  >
>  > From: aminreza Aamini <amin.r.fan at gmail.com>
>  > Subject: [R] Relative Risk in logistic regression
>  > To: "R-help" <R-help at r-project.org>
>  > Date: Wednesday, 30 January, 2013, 4:19 PM
>  >
>  >
>  > Hi all,
>  > I am very grateful to all those who write to me
>  > 1) how i  can  obtain relative risk (risk ratio) in logistic
> regression in R.
>  > 2) how to obtain  the predicted risk for a certain individual using
>  > fitted regression model in R.
>  >
>  > Many thanks, in advance, for your help.
>  >
>  > Amin.
>  >
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>


-- 
Kevin E. Thorpe
Head of Biostatistics,  Applied Health Research Centre (AHRC)
Li Ka Shing Knowledge Institute of St. Michael's
Assistant Professor, Dalla Lana School of Public Health
University of Toronto
email: kevin.thorpe at utoronto.ca  Tel: 416.864.5776  Fax: 416.864.3016


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