Question about permutation testing of an interaction in a two by two design
Stephan Moratti
moratti at MED.UCM.ES
Tue Nov 24 10:19:43 CET 2009
Hi all,
Thanks for the interesing discussion about the interaction with respect to
permutation. I have been also struggling with this question. As we want to
test the interaction (and not the main effect condition), I am not sure if
resampling condition would produce the distribution of our null hypothesis.
Regarding the interaction, we want to check if the mean values across
conditions follow the same pattern in two groups (if we consider a group x
condition interaction). If we make a line plot an interaction would be indicated
by a line crossing if each line represents a group (ideally). No interaction
would be represented by parallel lines for each group. So I wonder if by
resampling the subject values between the groups keeping the condition
structure intact, would create our null distribution for the interaction. If we
resample condition, we would destroy the condition structure.
What do you think? I would be happy for any input.
Best,
Stephan
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