# FBA-Vey Low Number of Fixels

**URL:** <https://community.mrtrix.org/t/fba-vey-low-number-of-fixels/2474>\
**Category:** Uncategorized\
**Created:** [April 25, 2019, 5:16pm UTC](https://community.mrtrix.org/t/fba-vey-low-number-of-fixels/2474 "2019-04-25T17:16:36Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![cmid](https://community.mrtrix.org/user_avatar/community.mrtrix.org/cmid/32/1684_2.png) [@cmid](https://community.mrtrix.org/u/cmid)\
**Post date:** [April 25, 2019, 5:16pm UTC](https://community.mrtrix.org/t/fba-vey-low-number-of-fixels/2474/1 "2019-04-25T17:16:37Z")

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Hi All,

I have processed muti-tissue FBA analysis ([http://userdocs.mrtrix.org/en/latest/fixel\_based\_analysis/mt\_fibre\_density\_cross-section.html](http://userdocs.mrtrix.org/en/latest/fixel_based_analysis/mt_fibre_density_cross-section.html)) on a multi-shell DTI data. Everything worked pretty well but I got a very low number of fixels (80170). Also, I didn’t get a group difference even with extremely very low significance (p=0.5). Could you please help me with that?

Thanks,  
Cmid

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**Author:** ![rsmith](https://community.mrtrix.org/user_avatar/community.mrtrix.org/rsmith/32/2672_2.png) [@rsmith](https://community.mrtrix.org/u/rsmith)\
**Post date:** [May 24, 2019, 1:50pm UTC](https://community.mrtrix.org/t/fba-vey-low-number-of-fixels/2474/2 "2019-05-24T13:50:53Z")

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Hi Cmid,

> I got a very low number of fixels (80170)

Did you use the same spatial resolution as what is described in the online documentation? As well as fixel segmentation thresholds? You will need to take a closer look at the data to assess what feature(s) of your data may be leading to this number being different from what is expected.

> Also, I didn’t get a group difference even with extremely very low significance (p=0.5). Could you please help me with that?

Sometimes there isn’t a group difference? 🤷‍♂️ Alternatively the low fixel count may be indicative of some more fundamental issue, which would obviously need to be rectified before interpreting the presence or absence of any statistically significant effect.

Rob