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From |
Morten Støver <morten.stover@ntnu.no> |

To |
Carlo Lazzaro <carlo.lazzaro@tin.it> |

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

Date |
Wed, 28 Sep 2011 14:43:16 +0200 |

If I "translate" my code it could look something like:

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 * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

-- Morten Støver PhD research fellow Department of Public Health and General Practice Norwegian University of Science and Technology

* * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**st: R: How to "reverse" log transformed result***From:*"Carlo Lazzaro" <carlo.lazzaro@tin.it>

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