help > Discrepancy between NiiStat and MRIcron NPM
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Nov 2, 2017  07:11 PM | Juan Dominguez
Discrepancy between NiiStat and MRIcron NPM

Signs of Z scores I am getting when running VLSM analysis in NiiStat and MRIcron NPM are reversed. Areas of significance are almost identical but the Z scores are positive in MRIcron NPM and negative in NiiStat. I have used the same design/parameters and behavioural scores in both cases. The documentation of NiiStat and MRIcron would indicate behavioural scores are interpreted the same in both packages (higher scores mean better performance) and therefore I would expect the sign of Z scores in both packages to coincide.

Could you please provide clarification on this issue?

I thank you in advance for your help.


Jun 21, 2018  09:06 AM | Chris Rorden
RE: Discrepancy between NiiStat and MRIcron NPM
1.) Please refer to the NiIStat notes: the polarity of NiiStat is reverse of VLSM/NPM. Rather, NiiStat follows the standard statistical convention that a positive association means that a brighter image correlates with higher behavioral scores. We tend to draw lesions as bright voxels (1) on a black (0) background. The reason for the change is that NiiStat is designed for many modalities (CBF, MD, FA) and therefore keeping the standard statistical mode makes sense