# FBA: pFWE and Puncorrected don't exactly match

**URL:** <https://community.mrtrix.org/t/fba-pfwe-and-puncorrected-dont-exactly-match/2912>\
**Category:** Uncategorized\
**Created:** [October 14, 2019, 4:07pm UTC](https://community.mrtrix.org/t/fba-pfwe-and-puncorrected-dont-exactly-match/2912 "2019-10-14T16:07:01Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![anege](https://community.mrtrix.org/letter_avatar_proxy/v4/letter/a/bbe5ce/32.png) [@anege](https://community.mrtrix.org/u/anege)\
**Post date:** [October 14, 2019, 4:07pm UTC](https://community.mrtrix.org/t/fba-pfwe-and-puncorrected-dont-exactly-match/2912/1 "2019-10-14T16:07:01Z")

</div>

Dear MRtrix experts,

I run FBA and when visualizing the results, I realized that some areas with lowest pFWE values are not the areas with lowest puncorrected. Does it make sense?

This is the image with lowest pFWE values:

 ![image](https://community.mrtrix.org/uploads/default/original/2X/e/e78bbac07d621ba91ae6159c79e63cfd089918d6.jpeg)

And this is the image with puncorrected\<0.01(1-p in the visualization tool)

 ![image](https://community.mrtrix.org/uploads/default/original/2X/a/a375fcdc5d59bb1866257130b283878c10d577c6.jpeg)

Shouldn’t they match?

Thanks in advance,  
Ane

---

<div class="post-metadata">

**Author:** ![jdtournier](https://community.mrtrix.org/user_avatar/community.mrtrix.org/jdtournier/32/2594_2.png) [@jdtournier](https://community.mrtrix.org/u/jdtournier)\
**Post date:** [October 15, 2019, 2:26pm UTC](https://community.mrtrix.org/t/fba-pfwe-and-puncorrected-dont-exactly-match/2912/2 "2019-10-15T14:26:39Z")

</div>

No, they wouldn’t be expected to match. The puncorrected values report the per-fixel _p_-values with no attempt to correct for multiple comparisions. In contrast, the pFWE report the _p_-values after correction for multiple comparisons, which involves the whole [connectivity-based fixel enhancement](https://www.ncbi.nlm.nih.gov/pubmed/26004503) framework, which enhance the _t_-values based on neighbourhood support: the higher the _t_-values in a given fixel’s neighbourhood, the higher the level of enhancement. So the pFWE values are not simply a scaled version of the puncorrected values. Regions with low puncorrected values may well end up with high pFWE values if they are part of a large neighbourhood where the effect is consistent – and _vice versa_. See the manuscript linked above for details.