hi,Tom,
Is the corrected P value from your code meaning the P is for the cluster after the whole brain correction? How can i calculate a corrected P value of a voxel after the correction of a hypothesis region (e.g., suppose this region includes 1000 voxels)?
thanks and best,
hengyi rao
[log in to unmask]
Department of Neurology
University of Pennsylvania
----------------------------
>Kenneth,
>
>On Thu, 1 Sep 2005, Sung Lai Yuen wrote:
>
>> I have a naive question regarding the omnibus test. I know in the
>> SPM results display we could find the voxel, cluster, and set level
>> p-values for a particular study. Nevertheless, if I decided to adopt
>> a particular height & extend threshold, e.g. uncorrected p=0.0005,
>> extend=16, how could I get the equivalent thresholding p-value at
>> the cluster level? Are there any equations/tables available for the
>> quick conversion?
>
>To get the corrected cluster P-value for a 16 voxel cluster with an
>uncorrected P-value threshold 0.0005, use this snippet
>
> load SPM
>
> k = 16; % cluster size
> u = spm_invTcdf(1-0.0005,df); % uncorrected 0.0005 thresh
>
> df = [1 SPM.xX.erdf]; % DF
> STAT = 'T'
> R = SPM.xVol.R; % Resels
> FWHM = SPM.xVol.FWHM;
> v2r = 1/prod(FWHM(~isinf(FWHM))); %-voxels to resels factor
> n = 1;
>
> P = spm_P_RF(1,k*v2r,u,df,STAT,R,n) % Corrected cluster P
>
>I'm not sure this answers your question though...
>
>-Tom
>
>
> -- Thomas Nichols -------------------- Department of Biostatistics
> http://www.sph.umich.edu/~nichols University of Michigan
> [log in to unmask] 1420 Washington Heights
> -------------------------------------- Ann Arbor, MI 48109-2029
>
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