temporal autocorrelation with lme
Dear all, I'm trying to fit lme models on spatial-temporal data with strong inter-annual autocorrelation. The response variable is a bird diversity measure sampled on several plots during 10 to 40 years, which I want to relate to environmental covariates. To give an idea of the sample size, there are appr. 800 plots. Here is the temporal autocorrelation of the response variable (averaged over years, x axis=years) Based on AIC, the best model I tried is a model with a corAR1 structure, as compared with ARMA models with different p and q lags. x1=corAR1(form=~year | plot) m2=lme(y~cov1+cov2+cov3,random=list(plot=~1),correlation=x1,data=d1) Below are residual plots. The first plot is a plot of residuals over years, the 2nd and third are plots of mean residuals per year vs years. The third plot is from the acf function. Looks like the AR structure does not correct temporal autocorrelation, and the ARMA models don't do better. I've tried other things, including adding a "year" covariate to remove the apparent linear trend, without making it with a better correction. Any advice or alternative solution? Many thanks, Best JYB
Jean-Yves Barnagaud Vertebrate Biogeography & Ecology group EPHE - CEFE - Montpellier, Fr. +0033(0)467613326 http://sites.google.com/site/jybarnagaud