multiple comparison of interaction of ANCOVA

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On Mon, Dec 12, 2011 at 7:00 AM, Jinsong Zhao <jszhao at yeah.net
<mailto:jszhao at yeah.net>> wrote:

    Apart from the data set here, is there a way to do multiple
    comparison on the interaction of one way analysis of covariance?

Interaction in ancova usually means the slopes are different.
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A better solution is to use glht in the multcomp package instead of
TukeyHSD.
Then the statement is
     confint(glht(mydata.aov, linfct=mcp(Trt="Tukey")))
glht is better because it does not have the limitations of TukeyHSD.
TukeyHSD is not applicable in your example because TukeyHSD doesn't work
with covariates.
The documentation ?TukeyHSD says "non-factor terms these will be dropped
with a warning".
With glht and the HH package loaded, you can get a better plot.
     glht.mmc(mydata.aov, linfct=mcp(Trt="Tukey"))
     plot(glht.mmc(mydata.aov, linfct=mcp(Trt="Tukey")))
With the MMC plot ?HH:::MMC, "Each contrast is plotted at a height which
is the weighted
average of the means being compared"