@allmaktub I think for group analysis ft_sourcestats takes into account the paired sample t-test (dependent sample) and to run paired t-test you need to select equal number of files in process 2 of Brainstorm. You can select the same number of files either by Run>Files>Select uniform files or you can simply delete the files from File A or File B in the process 2. It will not delete your original files but will reduce the number of files in the process 2.