How can I perform a TukeyHSD with continuous and categorical variables?
I am trying to perform a TukeyHSD post-hoc test on my data. I have some variables that are categorical and one variable that is a numerical continuos variable (it represents different ranges of altitude, so the 1 refers to the range 1000-1100, the 2 refers to 1101-1200 and so on).
When I try to perform the Tukey test I get an error.
The code I used is the following: TukeyHSD(model1, "var1:var2:var3:var4:var5", conf.level = .95)
where var5 is the continuous one.
The error I get is the following: In qtukey(conf.level, length(means), x$df.residual) : NaNs produced
What could be the problem?