Hi, let's say I have a simple ANOVA model with 2 factors A (level A1 and A2) and 
B (level B1 and B2) and their interaction:

aov(y~A*B, data=dat)

It turns out that the interaction term is not significant (e.g. P value = 0.2), 
but if I used glht() to compare A1 vs. A2 within each level of B, I found that 
the comparison is not significant when B=B1, but is very significant (P<0.01) 
when B=B2.

My question is whether it's legal to do this post-hoc comparison when the 
interaction is NOT significant? Can I still make the claim that there is a 
significant difference between A1 and A2 when B=B2?

Thanks

John



      
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