# SDM calculations

## Family-wise error correction

The family-wise error correction is attained by running a subject-base permutation test and obtaining a distribution of the maximum statistic. This distribution is then used to threshold the meta-analysis images obtained in the Mean or Linear Model calculations, resulting in a corrected p-values map.

### To calculate a FWE

Press the button [FWE]

*or*

Select [FWE] in the *Statistics* menu, to open the following dialog:

### Multi-threading

The calculation of the distribution step of the FWE calculation, which **will** take long in
any meta-analysis, can be run in parallel using concurrent threads. **Note:**
is not advisable to use more concurrent threads than the available in
your pc. You can learn the number of available threads in your pc at the
'multithreading' tab of the preferences windows.

### Command-line and batch usage

perm *number_of_permutations,model_name* where the model_name is the name of a model for which a Mean or Linear Model has previously been calculated.

*Example:*

perm 1000,model_name

**Note:** In order to modify the number of concurrent threads while using the command-line, you need to modify by hand the value of *nthreads* in the section (xml tag **after** the Mean or Linear Model is calculated.

### References

(current method):
Albajes-Eizagirre A, Solanes A, Vieta E *and*
Radua J. Voxel-based meta-analysis via permutation of subject images (PSI): Theory and implementation for SDM.
*NeuroImage* 2019; 186:174.

Winkler A M, Ridgway GR, Webster MA, Smith SM *and*
Nichols TE. Permutation inference for the general linear model.
*Neuroimage* 2014; 92:381-397.