I received also this message that did not show up here:

This sounds like a problem in (linear) mixed effects models. Look into
packages
nlme (with the lme() function) and lme4 (function lmer()) for starters. What
you
have falls under the heading of longitudinal or repeated measures data. Both
packages allow flexibility in the choice of within-unit covariance
structure.

 

It seem that it is trickier than it seems. I cannot test the
gls(density~year*stream,..) as I do not have replicates within stream, but
only one measurement for each stream. I tried to compare via anova the two
models:

Mixed1 <- lme(density~year, data=mydata, random=~1|sector)

Mixed2 <- lme(density~year, data=mydata, random=~1|year/sector)

 

But I'm not sure I can fit the Mixed2 model.

Many thanks for the answers so far.

Any ideas?

 

 

Simone Vincenzi, PhD 
Department of Environmental Sciences
University of Parma
Viale G. P. Usberti, 33/A, 43100 Parma, Italy
Phone: +39 0521 905696
Fax: +39 0521 906611
e.mail:  <mailto:svincenz@nemo.unipr.it> svincenz@nemo.unipr.it

 


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