[R-sig-eco] log link versus log response 2

[ONKELINX, Thierry]

Tomas,

What I would do is calculate the median and a confidence interval in the
transformed space. Since the log transformation is a monotone
transformation it will preserve the order of the values. So the median
stays the median, the 2.5% quantile stays the 2.5% quantile and so on.
But be aware that while in the transformed space the median equals the
mean (= the prediction), this will not hold when you backtransform the
values to the original scale.

HTH,

Thierry

------------------------------------------------------------------------
----
ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature
and Forest
Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
methodology and quality assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium 
tel. + 32 54/436 185
Thierry.Onkelinx at inbo.be 
www.inbo.be 

To call in the statistician after the experiment is done may be no more
than asking him to perform a post-mortem examination: he may be able to
say what the experiment died of.
~ Sir Ronald Aylmer Fisher

The plural of anecdote is not data.
~ Roger Brinner

The combination of some data and an aching desire for an answer does not
ensure that a reasonable answer can be extracted from a given body of
data.
~ John Tukey

-----Oorspronkelijk bericht-----
Van: r-sig-ecology-bounces at r-project.org
[mailto:r-sig-ecology-bounces at r-project.org] Namens Tomas Easdale
Verzonden: donderdag 24 april 2008 5:24
Aan: r-sig-ecology at r-project.org
Onderwerp: [R-sig-eco] log link versus log response 2

Thanks Scott, 

That response is very useful and it all makes sense now as LOG
transforming the response works better for heterocedastic data. But your
response also brings me to a second question that has been circulating
around. What can/should I do if I want to use my regression to predict
responses in the original scale. Exponentiate the errors? That doesn't
seem much feasible, is it? 

Cheers
Tomas
   


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