SPSS N-way AN?OVA -> R ? (was [R] Unbalanced ANOVA in R?)
Fredrik Karlsson
fredrik.karlsson at ling.umu.se
Fri Mar 8 14:34:19 CET 2002
Thank you Professor Ripley for the quick and informative response.
Being unable to choose a different textbook (even though I must admit
that this SPSS obsession is starting to annoy me).
I solved the problem though.
I changed the subject for this post in order to change the topic into
a more general one:
What does aov() do and what does it NOT do?
Prof. Ripley mentioned that you should use the lme() function for
multistrata anova, so that's one. What else? (Realising that this is a
question with an open set of answers).
My impression is that what I am suppose do do in SPSS under some heading
n-way anova, ancova, one-way glm or whatever is handled in S/R by aov()
Does this mean you can use aov() to compare two groups with different
ns?
Many open questions, I know, but the SPSS -> R translation is troubling
for me.
Please, could someone sort this out for me?
/Fredrik
On Fri, Mar 08, 2002 at 06:24:27AM +0000, Prof Brian D Ripley wrote:
> On Fri, 8 Mar 2002, Fredrik Karlsson wrote:
>
> > Hi all
> >
> > I'm trying to complete a textbook example originally designed for SPSS
> > in R, and I therefore need to find out how to compute an unbalanced
> > ANOVA in R.
> >
> > I did a search on the mailinglist archives an found a post by Prof.
> > Ripley saying one should use the lme function for (among other things)
> > unbalanced ANOVAs, but I have not been able to use this object.
> > My code gives me an error.. Why is that ?
> >
> > > aov(lme(DELAY ~ DOSE + TRIALS,data=epinuneq))
> > > Error in getGroups.data.frame(dataMix, groups) :
> > > Invalid formula for groups
> >
> > Any ideas? How do I get an ANOVA computation that can handle uniqual
> > sampe sizes in R?
>
> I said use lme, *not* aov and lme. Note, though, that the advice applied
> to multistrata unbalanced anova, and this appears to be a two-way layout in
> one stratum. You can use aov for that. (You can't use lme unless there are
> two or more strata.) Just be careful how you interpret the output: in SAS
> parlance aov gives you `Type I' sums of squares.
>
> The reason why this is more difficult in R is that R unlike SPSS does not
> guess which of the many possible interpretations you mean. We would need
> to know a lot more about the actual statistical problem to tell you what
> would be a good analysis in R.
>
> Maybe you should look at a textbook designed for use with S/R not SPSS?
>
> --
> Brian D. Ripley, ripley at stats.ox.ac.uk
> 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 272860 (secr)
> Oxford OX1 3TG, UK Fax: +44 1865 272595
>
>
--
-----------------------------------------------------------------
Fredrik Karlsson, Research Student
Department of Philosophy and Linguistics
Umeå University
S-901 87 UMEÅ
SWEDEN
Tel: +46 90 786 56 84 Web: http://www.ling.umu.se/~fredrik/
Fax: +46 90 786 63 77 Email: fredrik at ling.umu.se
PGP-fingerprint:2DD5 54A1 4555 6D00 F386 C269 C430 0C0F 1A53 49B9
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