cluster-based permutation tests on single subjects

[Eric Maris]

Hi Tim,



> I have a few related questions about Maris and Oostenveld's (2007) method
for
> cluster-based permutation tests, in particular using an indepsamplesT
statistic in a
> between-trials design on single subjects.
> 1. Is it problematic to have very different numbers of trials within each
condition?

No, it is not.

> 2.  Any advice for calculating statistical power for different numbers of
trials within
> each condition?

I'm not sure whether I understand what you mean. Anyhow, analytical
statistical power calculation (as is possible for T-tests and anovas) are
not possible for permutation tests. However, one can obtain Monte Carlo
estimates of power using simulations under the alternative hypothesis.


> 3. Might it be advisable to somehow trim the trials (e.g., Leonowicz,
Karvanen, &
> Shishkin, 2005) to remove outliers prior to analysis?

This may increase your sensitivity. However, to obtain sound p-values, you
must do trimming in a way that does not induce differences between the
experimental conditions.


Best,

Eric Maris




>
> Any advice would be much appreciated.
> thanks
> Tim
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----------------------------------
The aim of this list is to facilitate the discussion between users of the FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html and http://www.ru.nl/neuroimaging/fieldtrip.