Re: st: Transformed values in logistic regression

[Ronán Conroy <rconroy@rcsi.ie>]

Ricardo Ovaldia wrote:

> Specifically we were interested in modeling
> case-control status as a function of several patient
> covariates including serum creatinine which in our
> data ranges from 0.11 to 1.98.
> Because of skewness and to make the odds ratio
> independent of the units measurement, we decided to
> log-transform the creatinine values before entering
> them into our logistic model. However the reviewer
> wrote “Using a log-transform for creatine is absurd
> because a 1-unit increase in ln(x) is equivalent to
> increasing x by a factor of 2.718 which is in the
> realm of impossibility”
>  
I would try expressing creatinine in deciles. This gives a more 
intuitively appealing measure than taking the log. You can also output, 
using -adjust- predicted values for, say, the first and last deciles, 
which give a clear idea of how important creatinine is in your model.
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