[R] Relative Risk in logistic regression
Frank Harrell
f.harrell at vanderbilt.edu
Thu Jan 31 15:42:16 CET 2013
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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