[R] Help with short time series
Simone Vincenzi
simone.vincenzi at nemo.unipr.it
Mon Aug 7 22:07:21 CEST 2006
Thanks for the help.
I provide below the dataset I'm using, it's a little bit different from what
I was describing (sorry for that). The streams are 3 and I have an unequal
number of years for each stream.
Stream Density Year
1 Zak 0.20 2000
2 Zak 0.36 2001
3 Zak 0.41 2002
4 Zak 0.34 2003
5 Zak 0.28 2004
6 Gor 0.08 1999
7 Gor 0.05 2000
8 Gor 0.14 2001
9 Gor 0.16 2002
10 Gor 0.13 2003
11 Gat 0.18 2004
12 Gat 0.10 2001
13 Gat 0.37 2002
14 Gat 0.57 2003
15 Gat 0.47 2004
I tried to follow the suggestions of Dieter, but the model does not fit.
Any suggestion will be appreciated
Dear R-list,
> I have a statistical problem with the comparison of two short time-series
of
> density data in an ecological framework. I have to compare two short time
> series (5 years, one value for each year) of species density data (it is
the
> density of fish in two different streams) to test if the two means of the
> five densities are significantly different, so basically if the two mean
> stream-specific fish densities are significantly different.
> I don't think I can use a straight t-test due to the problem of
> autocorrelation and I don't think I can use a repeated measure ANOVA as I
> don't have any replicates.
> Any help would be greatly appreciated.
try something like
library(nlme)
summary(lme(dens~stream+year,data=mystreamdata,random=~year|stream))
This should also give you an estimate if the slopes are different if you
test
against the simplified model
summary(lme(dens~stream+year,data=mystreamdata,random=~1|stream))
Since you did not provide a short example data set, this is only
approximatively
right.
Dieter
--
Universita' degli Studi di Parma (http://www.unipr.it)
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