R help - Apr 2009 - Anova interaction not tested

I've noticed with certain datasets that when I try to do an anova and test
for main effects and interaction for two explanatory variables, sometimes
the main effect results are given but not the interaction results. For
example,

ex1 = aov(Score ~ var1*var2, data=myData)
summary(ex1)

gives me only the main effects for var1 and var2, but not the interaction. I
also tried

ex1 = aov(Score ~ var1+var2+var1:var2, data=myData)
summary(ex1)

but it still only gives the main effects. The only way I can get the
interaction results is if I test for ONLY that, e.g.

ex1 = aov(Score ~ var1:var2, data=myData)
summary(ex1)

Why would the interaction not be tested in the first two examples?

Thanks,
Gabe

	[[alternative HTML version deleted]]

On Wed, 08-Apr-2009 at 12:59PM -0700, Gabriel Murray wrote:

|> I've noticed with certain datasets that when I try to do an anova and
test
|> for main effects and interaction for two explanatory variables, sometimes
|> the main effect results are given but not the interaction results. For
|> example,
|> 
|> ex1 = aov(Score ~ var1*var2, data=myData)
|> summary(ex1)

Could it be that there are no degrees of freedom left?

That's about my best guess without enough information.


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Nothing you sent is reproducible.


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