[R] Relative Risk in logistic regression

[Frank Harrell]

I am curious why one would want risk ratios.  Unlike odds ratios, they are
not interpretable without reference to the base risk.  For example a risk
ratio of 2 cannot possibly apply to anyone with a starting risk exceeding
1/2.

I think it is most helpful to use one of the existing nomograms to show
someone how the base risk and odds ratio translate to final risk, for a
range of base risk.

Frank

David Winsemius wrote
> On Jan 30, 2013, at 5:49 AM, aminreza Aamini wrote:
> 
>> 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.
> 
> You obtain the predicted probabilities with something like:
> 
> predict(model, data.frame(x1="a", x2=30), type = "response")
> 
> See ?predict.glm
> 
> This would give the odds ratios (similar but larger than the risk  
> ratios):
> 
> exp(coef(model))
> 
> -- 
> David Winsemius, MD
> Alameda, CA, USA
> 
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-----
Frank Harrell
Department of Biostatistics, Vanderbilt University
--
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