No, the question asked was how to run a non-parametric test & the answer of
converting to ranks is a correct procedure (amongst various other
non-parametric procedures). You're presenting a different issue entirely.
Your statements below are correct that converting to ranks changes the
null-hypothesis, and therefore the ranks may show an interaction where the
raw data do not (or vice versa); and some other procedure may be preferable
to a rank-transformation.
----- Original Message -----
From: "Fortunato Pesarin" <[log in to unmask]>
To: "Jeff Rasmussen" <[log in to unmask]>
Sent: Friday, April 12, 2002 3:54 AM
Subject: Re: FW: non parametric problems
> Dear colleagues,
>
> the idea to convert data into ranks and then run a regular 3-way anova is
> incorrect. In fact the rank transformation may induce apparent
interactions
> where there are none, or may hidden interactions or even main effects
where
> they are present.
> One possibility is to run "syncronized permutations" as they are described
> in chapter 8 of my book: F. Pesarin, Multivariate Permutation tests with
> Applications in Biostatistics, Wiley, Chichester (2001).
> With regards,
> F. Pesarin
>
>
> At 07.21 11/04/02 -0500, you wrote:
> >Just convert the data to ranks and then run a regular 3-way anova.
> >
> >
> >----- Original Message -----
> >From: "Shirley Coleman" <[log in to unmask]>
> >To: <[log in to unmask]>
> >Sent: Thursday, April 11, 2002 3:42 AM
> >Subject: FW: non parametric problems
> >
> >
> >> Any ideas , please?
> >>
> >>
> >>
> >> I have been approached by a postgrad who has collected scored data from
a
> >> 3-way factorial experiment. There are only 9 classes and usually the
> >> replicates all have the same result. As you can imagine the residuals
are
> >> not normally distributed. Do you happen to know of a three-way
> >> non-parametric test that will let me also check the interactions
between
> >> the treatments?
> >>
> >
> >
> Prof. Fortunato Pesarin
> Department of Statistics
> University of Padova
> via Cesare Battisti, 241/243
> 35121 PADOVA - ITALY
> Tel. +39.049.8274143
> Fax +39.049.8274170
> email: [log in to unmask]
> Web page: www.stat.unipd.it/~pesarin
>
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