Asking, are simple effects different from 0

Indeed, but are not each of the cell means also evaluations of the effect of
one factor at the specific level of another factor?  Is this an issue of
"Tomato, tomahto".

I guess my question is, if I want to know if each of those is different from
0, then should I use the 48df from the full model, or the 9 for each cell?

Chuck Cleland wrote:

   That does not corresponds to what I think of as the simple effects. 
That specifies the six cell means, but it does not *compare* any cell 
means.  I think of a simple effect as the effect of one factor at a 
specific level of some other factor.

summary(glht(fm, linfct = cm2), test = adjusted(type="none")) 

Correct? What is the df on those t-tests then?  Is it 48?

   Yes, df = 48 for each contrast.

Interestingly, I find this produces results no different than

fm2<-lm(breaks ~ tension:wool+0, data=warpbreaks) 
summary(fm2)

   Yes, but those are not what I would call the simple effects.  Those 
are essentially one-sample t-tests for each of the 6 cell means.

Also, here, it would seem each t-test was done with the full 48df.  Hrm.

   The df are based on the whole model, not the 9 observations in one
cell.