Hi Or, I understand your question (and am not sure what the confusion is about actually). Just like you said, you want to know the effect of A at B=1, and the effect of A at B=2. In this case, you want to know if drug has a significant effect for those with strain one, and whether drug has a significant effect for those with strain two. So the good part is, I understand the question.
The bad part is that unfortunately I don't know how to do it with aov(). Also, I'm not a stats guru and could easily be wrong about the following advice. You've been warned! If you didn't have a mixed model, I would tell you to run the model using lm() twice, setting drug = 1 as the reference group the first time, and drug = 2 as the reference group the second time, but this won't work in your case. The best I can offer is a suggestion to run the model separately for each level of drug. Note that you can and should use the error term from the overall model though -- you will have to do this "by hand" (just divide MS_effect from the subset model by MS_error from the full model, and evaluate using df_error from the overall model). So basically, I'm suggesting that you do Data.drug1 <- subset(Data, drug == "1") aov.model.drug.1 <- aov(dependent~(exposure*strain) + Error(subject/exposure) + (strain), data=Data.drug1) summary(aov.model.drug.1) Data.drug2 <- subset(Data, drug == "2") aov.model.drug.2 <- aov(dependent~(exposure*strain) + Error(subject/exposure) + (strain), data=Data.drug2) summary(aov.model.drug.2) Good luck! -Ista On Sun, Dec 20, 2009 at 11:35 AM, Or Duek <ord...@gmail.com> wrote: > For some reasion I wasn't able to use TukeyHSD - I think because I need to > set the different levels under a second variable. > Tukey only helps me when I have more than 2 levels of same variable. > Thanl you. > On Sun, Dec 20, 2009 at 6:32 PM, S Devriese <sdmaill...@gmail.com> wrote: > >> On 12/20/2009 04:56 PM, Or Duek wrote: >> > I don't have missing data. >> > about what I need. >> > Lets say the drug*strain interaction is significant - now I want to check >> > for drug under the levels of strain - compare drug 1 and 2 only on strain >> 1 >> > and then only on strain 2. >> > Or I'd like to compare the strains under levels of exposure. >> > This is the kind of data I fail to see in summary() but it is important >> to >> > understand the interactions. >> > thank you. >> > >> >> Do you main pairwise multiple comparison tests like Tukey Honest >> Significant Difference tests? Then you could use TukeyHSD in the stats >> package or see the DTK package (Dunnett-Tukey-Kramer Pairwise Multiple >> Comparison Test Adjusted for Unequal Variances and Unequal Sample Sizes) >> >> Stephan >> > > [[alternative HTML version deleted]] > > ______________________________________________ > 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. > -- Ista Zahn Graduate student University of Rochester Department of Clinical and Social Psychology http://yourpsyche.org ______________________________________________ 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.
