Hi I am following the model building strategy that is outlined in the Pinheiro and Bates book wrt including covariates but am having a problem with the plot. Basically I am using 4 covariates (1 of them is continuous) and 3 of them are fine but the 4th one is being shown as a scatterplot despite the fact that it is a factor. I have explicitly declared this to be a factor (pcat<-as.factor(pcat)) and have also checked by using the "is.factor" and the "levels" command that it is a factor. Yet despite this the plot command is not recognising it as a factor. Any ideas? Many thanks Greg BTW I have 1st created an object that holds the random effects estimated by my model (D1C2.ran <- ranef(mod11.103nlme,augFrame=T)) and then it is this object that I try plot (plot(D1C2.ran,form= C ~site+mutcat2+pcat+pdens0). [[alternative HTML version deleted]]