I am trying to do and ANCOVA with ten sites that I want to compare condition at, with Length as a covariate. Most examples I have found only deal with two levels and I am unsure if the same code applies for more than two levels. Here is what I have, and I just wanted to double check that I am on the right track.... ancova<-lm(Condition~site+Length+site:Length) summary(ancova) anova(ancova) ancova1<-update(ancova,~.-site:Length) anova(ancova,ancova1) summary(ancova1) Any help/suggestions welcome! Thanks! -- View this message in context: http://r.789695.n4.nabble.com/ANCOVA-with-many-levels-of-one-factor-tp3991474p3991474.html Sent from the R help mailing list archive at Nabble.com.