[R] Help with short time series

From: Simone Vincenzi <simone.vincenzi_at_nemo.unipr.it>
Date: Wed 09 Aug 2006 - 07:44:49 EST

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
> 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
> 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


This should also give you an estimate if the slopes are different if you test
against the simplified model


Since you did not provide a short example data set, this is only approximatively


Universita' degli Studi di Parma (http://www.unipr.it)

Simone Vincenzi, PhD Student 
Department of Environmental Sciences
University of Parma
Parco Area delle Scienze, 33/A, 43100 Parma, Italy
Phone: +39 0521 905696
Fax: +39 0521 906611
e.mail: svincenz@nemo.unipr.it 



Universita' degli Studi di Parma (http://www.unipr.it)

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Received on Wed Aug 09 07:59:49 2006

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