R help - Jul 2009 - prevalence in logistic regression lrm()

Hi, I am wondering if there is a way to specify the prevalence of events in
logistic regression using lrm() from Design package? Linear Discriminant
Analysis using lda() from MASS library has an argument "prior=" that
we can use to specify the prevalent of events when the actual dataset being
analyzed does not have a representative prevalence. How can we incorporate this
information in lrm()? The concern I have is if my dataset does not have a
representative prevalence, then the probability generated by lrm() will not be
meaningful. Thanks

John

This is dangerous because prevalence is an ill-defined concept.  Most
discussions of prevalence fail to understand conditioning completely.

If you must, you can do this with an appropriate offset() term.

Frank

>
> Hi, I am wondering if there is a way to specify the prevalence of events
> in logistic regression using lrm() from Design package? Linear
> Discriminant Analysis using lda() from MASS library has an argument
> "prior=" that we can use to specify the prevalent of events when
the
> actual dataset being analyzed does not have a representative prevalence.
> How can we incorporate this information in lrm()? The concern I have is if
> my dataset does not have a representative prevalence, then the probability
> generated by lrm() will not be meaningful. Thanks
>
> John
>
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