Dear R-sig-Geo list, I've a question about a spatial regression model I'm working with. Here is my problem and question:
I'm modeling the local densities of a species (y) as a second order polynom of the geographical position (lon,lat), time (year), and a certain number of other variables: mod1 <- lm( y ~ ... + poly(lon,lat, degree=2)*as.factor(year)) Then, I know that the sampling has a certain spatial resolution, that I can represent with a regular grid. Thus, I was thinking that observations within the same cell of the grid (gr.id) cannot be considered completely independent, and that this could be represented with a random effect like: mod2 <- lme( y ~ ... + poly(lon,lat, degree=2)*as.factor(year), random=list(gr.id=~1)) An additional level of complexity within my formulation, is given by the temporal resolution. Thus, I would like to group the spatial dependency of observations from the same cell within certain time intervals (time.gr). Here my problem comes. I'm a bit confused on how to formulate exactly the random effect expressed above into time.gr groups. I have alternative slightly different formulations in mind, but I miss their difference in practice. Thanks in advance for any help or advice. Valerio -- Valerio Bartolino, PhD Institute of Marine Research - Swedish Board of Fisheries PO Box 4, 45321 Lysekil, Sweden Department of Earth Sciences - Gothenburg University PO Box 460, 40530 Göteborg, Sweden e-mail: valerio.bartol...@gvc.gu.se valerio.bartol...@gmail.com ><(((*> ----- ><(((*> ----- ><(((*> ----- ><(((*> _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo