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) _________________________________________ 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: [EMAIL PROTECTED] -- -- Universita' degli Studi di Parma (http://www.unipr.it) ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.