Geertje Van der Heijden wrote: >Hi, > >I am trying to calculate Moran's I test for the residuals for a >regression equation, but I have trouble converting my coordinates into >nb format. > >I have used the dnearneigh() funtion now with an arbitrarily high upper >distance to make it include all plots. However, when I do the >lm.morantest() I get a Moran's I value which is the same as the expected >value and a P-value of 1. > >I have used the following code: > > >>attach(lowland) >>coords <- as.matrix(cbind(long, $lat)) >>coord.nb <- dnearneigh(coords, 0, 10000 longlat=TRUE) >>coord.list <- nb2listw(coord.nb, style="W") >>lianasp.lm <- lm(lianasprich ~ log(averdist) + dsl + lianadens + >> >> >wooddens) > > >>lm.morantest(lianasp.lm, coord.list, alternative="two.sided") >> >> > >And get the following result > > Global Moran's I for regression residuals > >data: >model: lm(formula = lianasprich ~ log(averdist) + dsl + lianadens + >wooddens) >weights: coord.list > >Moran I statistic standard deviate = 0, p-value = 1 >alternative hypothesis: two.sided >sample estimates: >Observed Moran's I Expectation Variance > -1.754386e-02 -1.754386e-02 2.125706e-16 > >Can anyone tell me where I went wrong or if there is another way to >generate a nb list? > >Many thanks, >Geertje > > Hi,
did you have a look at the graph you produced (using plot.nb)? Maybe the maximum distance between any two neighbours is too high. What does max(dist(coords)) say ? Anyway, there are many different connection networks available in several R packages, some being more appropriate than others to model paticular spatial distributions. The package adegenet proposes a small tool to choose among several graphs interactively: library(adegenet) xy = matrix(runif(100),ncol=2) yourcn = chooseCN(xy) Regards, Thibaut. -- ###################################### Thibaut JOMBART CNRS UMR 5558 - Laboratoire de Biométrie et Biologie Evolutive Universite Lyon 1 43 bd du 11 novembre 1918 69622 Villeurbanne Cedex Tél. : 04.72.43.29.35 Fax : 04.72.43.13.88 [EMAIL PROTECTED] http://lbbe.univ-lyon1.fr/-Jombart-Thibaut-.html?lang=en http://pbil.univ-lyon1.fr/software/adegenet/ ______________________________________________ R-help@r-project.org 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.