Hi, How would one go about determining if the slope terms from an analysis of covariance model are different from eachother?
Based on the example from MASS: library(MASS) # parallel slope model l.para <- lm(Temp ~ Gas + Insul, data=whiteside) # multiple slope model l.mult <- lm(Temp ~ Insul/Gas -1, data=whiteside) # compare nested models: anova(l.para, l.mult) Analysis of Variance Table Model 1: Temp ~ Gas + Insul Model 2: Temp ~ Insul/Gas - 1 Res.Df RSS Df Sum of Sq F Pr(>F) 1 53 52.045 2 52 48.704 1 3.341 3.5673 0.06451 . It seems like this approach would yield insight into whether or not the two slope terms (InsulBefore:Gas and InsulAfter:Gas) were different. However, is there a formal test for this sort of question, and can it be generalized to differences between more than 2 slope terms? Thanks, Dylan -- Dylan Beaudette Soil Resource Laboratory http://casoilresource.lawr.ucdavis.edu/ University of California at Davis 530.754.7341 ______________________________________________ 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.
