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/>
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--
Brian D. Ripley, [EMAIL PROTECTED]
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
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