Greg, be careful using attach() and detach(). From the syntax snippets you showed it seems that you did create an object "pcat" ("factor variable"), but you did not change the respective "variable" in your data frame.
Try to remove "pcat" and see what happens do the results of lme()! Dirk ______________________________________________ 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.