birch <- read.table("http://www.stat.ufl.edu/~winner/data/birchpollen.dat", header=F,col.names=c("grn.diam","species","location")) attach(birch) species <- factor(species) location <- factor(location) birch.mod1 <- aov(grn.diam ~ species + species/location) anova(birch.mod1) birch.mod2 <- aov(grn.diam ~ species + Error(location)) summary(birch.mod2) library(lmerTest) birch.mod3 <- lmer(grn.diam ~ species + (1|species:location)) summary(birch.mod3) anova(birch.mod3) if(require(pbkrtest)) anova(birch.mod3, ddf = "Kenward-Roger") step(birch.mod3)