Thanks for getting back to me. i meant that i am seeking for a transformation of an s-shaped response (continuous data) to assure normally distributed residuals of the response. however, i am unsure if the "Let F be the distribution..." is now the correct thing for me to do. if this is the right thing to do, could you give me a hint how to code this that i can run the following model with the transformated response? my model: lme(fixed=Y~x1+ x2 + x3 , random=~ 1|Pond/Occasion, method="ML") thanks for your help. regards, lukas ________________________________
Von: Prof Brian Ripley [mailto:[EMAIL PROTECTED] Gesendet: Do 26.06.2008 08:45 An: Moshe Olshansky Cc: [EMAIL PROTECTED]; Indermaur Lukas Betreff: Re: [R] help_transformation On Wed, 25 Jun 2008, Moshe Olshansky wrote: > Let F be the distribution function of Y, PSI the standard normal > distribution anf IPSI it's inverse. Let f(x) = IPSI(F(x)). It is not > difficult to see that f(Y) has standard normal distribution. So you can > replace F with the empirical distribution and IPSI is the qnorm function > of R. Only if F is continuous, and 'some zero values' suggests that in this case that is not a reasonable model. I think there is a basic misunderstanding here: the response of a linear regression (including a mixed effects model) is not normally distributed: it is the Y[i] which are normally distributed under the usual model assumptions, but with different distributions. > > > --- On Wed, 25/6/08, Indermaur Lukas <[EMAIL PROTECTED]> wrote: > >> From: Indermaur Lukas <[EMAIL PROTECTED]> >> Subject: [R] help_transformation >> To: [EMAIL PROTECTED] >> Received: Wednesday, 25 June, 2008, 9:56 PM >> heya, >> i am fitting linear mixed effect model to a response Y. Y >> shows an s-shaped distribution when using QQ-plots (some >> zero values and some very high values). hence, which >> transformation should i apply that Y follows a normal >> distribution? any r-function/package available to do this? >> >> thanks for any hint, >> regards, >> lukas >> >> >> >> °°° >> Lukas Indermaur, PhD student >> eawag / Swiss Federal Institute of Aquatic Science and >> Technology >> ECO - Department of Aquatic Ecology >> Überlandstrasse 133 >> CH-8600 Dübendorf >> Switzerland >> >> Phone: +41 (0) 71 220 38 25 >> Fax : +41 (0) 44 823 53 15 >> Email: [EMAIL PROTECTED] >> www.lukasindermaur.ch <http://www.lukasindermaur.ch/> >> >> >> >> >> >> ______________________________________________ >> R-help@r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-help >> PLEASE do read the posting guide >> http://www.R-project.org/posting-guide.html >> and provide commented, minimal, self-contained, >> reproducible code. > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
