st: Re: R: How to "reverse" log transformed result

[Morten Støver <morten.stover@ntnu.no>]

About the multi-level piece: One of the things I will investigate is 
whether the time of the rehabilitation time varies between the 
municipalities.
If I "translate" my code it could look something like:
xtmixed logtime gender age unemployment i.diagnosis i.education, || 
municipality:, var


On 28.09.2011 14:04, Carlo Lazzaro wrote:
> Dear Morten,
> I do share the previous comments in that without knowing what you typed is
> difficult to advise.
> However, for what it worths, back transforming from a log transformation,
> the mean on the original scale can be obtained by exp(lm+lv/2), where lm and
> lv are the mean and the variance on the log scale, respectively.
>
> See as a useful reference: Briggs, A. and Nixon, R. and Dixon, S. and
> Thompson, S. (2005)Parametric modelling of cost data: some simulation
> evidence. Health Economics 14(4):pp. 421-428.
> http://eprints.gla.ac.uk/4151/.
>
> Kindest Regards,
> Carlo
>
>
> -----Messaggio originale-----
> Da: owner-statalist@hsphsun2.harvard.edu
> [mailto:owner-statalist@hsphsun2.harvard.edu] Per conto di Morten Støver
> Inviato: mercoledì 28 settembre 2011 9.41
> A: statalist@hsphsun2.harvard.edu
> Oggetto: st: How to "reverse" log transformated result
>
> I'm doing an multilevel linear regression analysis where I try to
> investigate  if there are variation in the lenght of the rehabilitation
> process before people are being granted a disability pension. I measure
> this in days, and since my data are very skewed, I've done a log
> transformation. Now I wonder how I can transform the results back to the
> original scale of measurement. As an example, this are the results for
> the different types of diagnosis.
> "Other" diagnosis:    (ref)
> Mental disorders:    0.1993938
> Musulosceletal:        0.0840664
>
> If I now try to transform the data back using di exp(.1993938) I get the
> result 1.2206626.
> If I try to analyse the data without log transforming them, I find that
> the mental disorders group have 166 days (95% CI: 75.5-265.6) longer
> rehabilitation time before being granted a disability pension than the
> "other" diagnosis group.
> I guess that the di exp is not the right way to transform the results
> back, but I don't know any other way to do it.
> I'm using Stata 11.
> Thank you for your help
>
>
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--
Morten Støver
PhD research fellow
Department of Public Health and General Practice
Norwegian University of Science and Technology
   

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