Interpreting fsl featquery output

Dear community,

I have performed a ROI analysis using fsl featquery. I noticed that in the output, different participants have different number of voxels (i.e., a different number in the #voxels column). I would like to ask two questions regarding that:

  1. Does the #voxels column represent the number of non-zero voxels in the mask? If so, could it be that different participants have different #voxels because some participants have signal dropout (i.e., voxels with no data)?

  2. if so, does the mean calculation (i.e., mean percent signal change column) takes it into account? that is, does featquery calculates the mean according to the specific number of non-zero voxels of each participant?

Thank you very much,