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Issue 5: exceedance probability: WARNING!
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Project Member Reported by jean.dau...@gmail.com, Jan 28, 2014
This thread is a warning on the use of exceedance probabilities (EPs).

By default, a RFX-BMS will try to compute exceedance probabilities using compiled C code for sampling on a Dirichlet distribution (spm_gamrnd.c). If the compilation has not been done, this attempt will fail and the toolbox will resort to a normal approximation of EPs.

The quality of this approximation increases with the ratio of number of subjects divided by the number of models. When this ratio gets smaller than one, the approximation can become slightly overconfident.

Note that the toolbox prompts the user with the following message: 'Warning: exceedance probabilities are approximated!'.


In such cases, users would be well advised to re-compile the code, so that 
EPs are correctly estimated. In some instances, it suffices to replace the files 'spm_gamrnd*.*' in the directory '/stats&plots/spm_code' with the attached files. If this does not work (if the warning message still appears), please follow this thread and we will find a solution.



spm_gamrnd.c
2.6 KB   Download
spm_gamrnd.mexmaci64
8.6 KB   Download
spm_gamrnd.mexw64
9.5 KB   Download
spm_gamrnd.mexa64
14.4 KB   Download
spm_gamrnd.mexglx
8.5 KB   Download
spm_gamrnd.mexmaci
12.6 KB   Download
spm_gamrnd.mexw32
7.0 KB   Download
Jan 28, 2014
Project Member #1 jean.dau...@gmail.com
Note: this may affect the beta testers of the multi-source version of the toolbox!
Jul 29, 2014
Project Member #2 jean.dau...@gmail.com
Exceedance probability: resolved.

The default sampling approach for EPs has now been changed to incorporate novel matlab's pre-compiled smapling routines. RFX-BMS only reverts to SPM sampling routines if VBA cannot find matlab's sampling routines.

NB: the new implementation using matlab's sampling routines is about 100 times faster (because it avoids loops)!




 

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