Hello

I have a question on how to perform a Duncan test after I set a model like this (see below).

The data consist of a dependent variable (PHt) and two dependent variables (REGION (3 levels) AND MANAGEMENT (3 levels)).


       MANAGEMENT
N      P    S
 REGION     A           196 196          196
                  V           196 196 196
                  H       196 196 196

196 is the number of trees on which PHt was estimated, but we cannot consider them as repetitions, they are subjects. Therefore, only one repetition per REGION*MANAGEMENT factor.

I set a two way ANOVA without repetition. Although within

model <- aov(PHt~REGION*MANAGEMENT+Error(subject_f/(REGION*MANAGEMENT)),data=obsHETf)

Then I try to run a Duncan test for REGION and also for MANAGEMENT. I get this error message.

Error in as.data.frame.default(x[[i]], optional = TRUE, stringsAsFactors = stringsAsFactors) :
  cannot coerce class "c("aovlist", "listof")" to a data.frame

Is there anyone who could give me a clue on what it is wrong? Maybe it isnot correct to call for a Duncan.test() for such type of model?

If I fit only the mean (mean of the 196 observations) within each REGION*MANAGEMENT factor, then Duncan.test() works as expected. The model then looks as simple as this.

model <- aov(PHt~REGION+MANAGEMENT,data=obsHET)

Thanks in advance.
R.


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