[Eeglablist] Bootstrap significance probability level

Christopher Summerfield summerfd at paradox.psych.columbia.edu
Wed Nov 2 05:29:41 PST 2005

dear Adrian, the familywise error rate can be calculated for bootstrap
stats in the following way:

1) calculate your statistics at every timepoint/voxel/whatever (we'll call
these 'point estimate statistics')
2) shuffle and permute
3) for each permutation, enter the *maximum* permuted value from across
all the sampled timepoints/voxels into a distibution
4) 'point estimate' statistics falling within the 95% confidence interval
of this distribution can be considered significant, adjusted for
familywise error.

for more information, see Burgess & Gruzelier, 1999
Methodological advances in the analysis of event-related desynchronization
data.	in Event-Related Desynchronization ed Gert Pfurtscheller, F H
Lopes Da Silva.

this process could be adapted to provdide false discovery rate correction
(see Genovese et al 2002).

good luck,

Christopher Summerfield
summerfd at psych.columbia.edu

On Mon, 31 Oct 2005, Adrian Guggisberg wrote:

> Hello
> I wonder, whether anyone has some practical considerations about which level
> of significance probability should be chosen for bootstrap statistics.
> Since we have to deal with multiple comparisons, the significance threshold
> should be decreased, but the question is how much. As much as I understand,
> the Bonferroni correction for multiple testing would correspond to a level
> of p < 0.05/(number of time points * number of frequency bins). However,
> this would require a very high amount of surrogate data.
> Most of the studies seem to use p-values < 0.01. What's the argumentation
> for this?
> In their J Neurosci Meth; 2004:9-21 Paper, Arnaud Delorme and Scott Makeig
> write that they have
> "implemented a method to fit the observed data distribution using a forth
> order distribution fit. This feature will be available in a near-term release
> of EEGLAB."
> Does this feature allow a significance level of 0.05? Is there a way to obtain
> it?
> Thank you very much for your help.
> Adrian Guggisberg, MD
> Neurologische Klinik und Poliklinik
> Inselspital
> CH-3010 Bern
> Switzerland
> _______________________________________________________________________
> Your Site for Swiss Maps: http://www.swissinfo-geo.org/
> _______________________________________________
> eeglablist mailing list eeglablist at sccn.ucsd.edu
> http://sccn.ucsd.edu/mailman/listinfo/eeglablist
> Eeglablist page: http://sccn.ucsd.edu/eeglab/eeglabmail.html
> To unsubscribe, send an empty email to eeglablist-unsubscribe at sccn.ucsd.edu

More information about the eeglablist mailing list