On Wed, Nov 21, 2012 at 8:16 PM, Yann Quide <[log in to unmask]> wrote:
> Dear Experts,
>
> I was wondering what can be a correct and accepted way to report an one-way between group ANOVA results.
>
> Let's say we have 3 different groups. To assess if there is any difference between them, we performed an one-way ANOVA (F-contrast [1 -1 0; 0 1 -1]).
>
> Here is my first question: is there a rule for thresholding this kind of analysis? Is a threshold of p=0.05 FWE too conservative?
>>> No. As long as you correct for multiple comparisons, the method really doesn't matter. Some people use voxel-wise FDR/FWE, some people use cluster-wise FDR/FWE, and some people use 3dClustSim in AFNI to establish extent thresholds.
>
> Our results show a significant cluster (even with a p=0.05 FWE threshold). In order to know what is the direction of this effect, we used separated (3) between-groups two-sample t-tests. In order to be consistent, we used the same threshold.
>
> Is that a good way to perform such an analysis?
>>>> Yes.
>
> Or would it be better, and less conservative, to use a different threshold, lest's say for exemple(and always trying to correct for multiple comparisons):
> - F-test: p=0.0001 uncorrected and reporting only clusters with a significant peak with FWE correction
> - post-hoc two-sample t-tests: p=0.0001 uncorrected at the voxel level but FWE corrected at the cluster level
>
> Does it make sense? Is there any methodological issue?
>>> I'd use the same thresholding method for both the F-test and post-hoc t-tests. Some researchers would also suggest that you correct for the number of post-hoc tests.
>
> Thanks for your comments/suggestions.
>
> Cheers,
>
> Yann
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