[R] Comparing means and trends in short time-series

[Dieter Menne]

Simone Vincenzi-2 wrote:
> 
>  I have a statistical problem with the comparison of short time-series,
> representing densities of fish in different streams. For each stream (6 in
> total, here below showed only part of the dataset) I have 8 years of
> density
> data, as follows:
> 
>  
>    year density stream
> 
> 1  2000 0.51  stream1
> 
> 2  2001 0.87  stream1
> Are mean densities different among streams from 2000 to
> 2007? Is it sufficient and appropriate a test of correlation (using rcorr
> of
> the library Design, for example) to test if density trends in time are
> similar among streams? 
> 
> 

Have a look at function gls in in package nlme.

gls(density~year*stream,....)

There are some similar examples in the book coming with nlme (chapter 5.4)

Dieter




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