[R] factor differences in anova
wouter.buytaert at tiscali.be
Mon Apr 14 16:07:21 CEST 2003
Well, it is a quite specific design: we want to see if there is
influence of sample location, topography and soil horizon (depth) on the
water retention of a set of soil samples. We have water retention points
of every sample at different pF tensions, and want to compare the
complete pF-curves. As there is of course a strong relationship between
tension (pF) and water content, my PhD director proposed this type of
Thanks for the help!
Katholieke Universiteit Leuven
On Mon, 2003-04-14 at 15:47, Prof Brian Ripley wrote:
> On 14 Apr 2003, wouter buytaert wrote:
> > Hello,
> > (maybe a quite basic statistical question, but I'm just struggling with
> > it)
> > I'm doing an anova:
> > > Res1<-aov(H2O~location+topo+horizon+pF+Error(location:topo:horizon))
> > (water retention of soils)
> > which gives a significant difference at factor "location".
> > Which function should I use to now which locations (there are 3: A, B
> > and C) differ significantly and which do not?
> Possibly TukeyHSD or package multicomp. However, we would need to know a
> bit more about the design, as that's a rather peculiar Error()
> specification and you would need to be careful to apply these functions in
> the right stratum (assuming the location effect only occurs in one).
> Function se.contrast would also be useful, and as there are only three
> pairwise differences, multiple comparison issues are going to be minor
> (especially as you have tested for an overall difference first).
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