[R] lm() and post hoc test

nutini.francesco at gmail.com nutini.francesco at gmail.com
Mon Jan 24 15:38:30 CET 2011

Dear Alex,
I have read your question about post-hoc test:

"Let's assume that according to Anova(lm(y~a*b, data=d)) the a:b interaction is significant, and I would like to know if there are specific combinations of a and b levels that differ from the control group. Are there any caveats against simply looking at the p-values in the output generated by summary(lm(y~a*b,data=d))? The documentation for summary.lm says nothing about multiple comparison correction, so I assume I need to do that myself, is that correct?"

I have the same problem about the interpretation of command "summary", and generically about the finest post-hoc test for implemented model with the code "lm()". I think that R-help is quite insufficient...
Which command did you use normally?

Thanks a lot,

Francesco Nutini

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