Eric Scott-3 wrote: > > I'm trying to do an ANCOVA with two factors (clipping treatment with two > levels, and plot with 4 levels) and a covariate (stem diameter). The > response variable is fruit number. The minimal adequate model looks like > this: > > model3<-lm(fruit~clip + plot + st.dia + clip:plot) > > I'd like to get some multiple comparisons like the ones from TukeyHSD, > but... > >
To quote glht: The mcp function must be used with care when defining parameters of interest in two-way ANOVA or ANCOVA models. Here, the definition of treatment differences (such as Tukey's all-pair comparisons or Dunnett's comparison with a control) might be problem specific. Because it is impossible to determine the parameters of interest automatically in this case, mcp in multcomp version 1.0-0 and higher generates comparisons for the main effects only, ignoring covariates and interactions (older versions automatically averaged over interaction terms). A warning is given. We refer to Hsu (1996), Chapter 7, and Searle (1971), Chapter 7.3, for further discussions and examples on this issue. ---- Too bad there is no example (Hi, Torsten.... it would be nice). A thread coming close is in: http://markmail.org/message/rhdohxlrt3cpsdpx Dieter -- View this message in context: http://n4.nabble.com/Multiple-comparisons-for-a-two-factor-ANCOVA-tp1593039p1593082.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ 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.