R help - Dec 2008 - post hoc comparisons of interaction means after lme

Dear Colleagues,
I have run the following two models, where category has 3 levels and comp
has 8 levels:

mod1 <- lmer(x~category+comp+(1|id),data=impchiefsrm)
mod2 <- lmer(x~category+comp+category*comp+(1|id),data=impchiefsrm)

followed by:

anova(mod1,mod2)

The anova shows that the interaction term specified in the second model is
significant.

Now I'd like to run post hoc comparisons using glht.  For example, I can
run:

summary(glht(mod2,linfct=mcp(category="Tukey")))

But this only gives me the mean comparisons for the "category" main
effect
means.  Essentially I'd like to run the following:

summary(glht(mod2,linfct=mcp(category*comp="Tukey")))

to get the mean comparisons for the interaction means.  Perhaps needless to
say, this command does not work.

Can someone tell me how to run multiple comparisons among the interaction's
means?

Thanks,

Larry

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