[R] TukeyHSD troubles
RICHARD M. HEIBERGER
rmh at temple.edu
Fri Feb 26 08:08:34 CET 2010
> treat_code is a dummy
> variable, but that shouldn't matter. Any suggestions?
It does matter to TukeyHSD. If treat_code is a numeric variable with discrete
values 0 and 1, then it does not have class "factor". It is true that
aov will give the same
ANOVA table for a two-level factor as for a two-value numeric. It will give
different ANOVA tables if there are more than two values. TukeyHSD will refuse
to do anything for a numeric variable. It insists on factors.
You must use the statement
mydata$treat_code <- factor(mydata$treat_code)
before creating the aov object that you give to TukeyHSD.
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