# ANCOM results: phyla with W values of 0 identified as differentially abundant

**URL:** https://forum.qiime2.org/t/ancom-results-phyla-with-w-values-of-0-identified-as-differentially-abundant/10647
**Category:** User Support
**Created:** [July 12, 2019, 9:31am UTC](https://forum.qiime2.org/t/ancom-results-phyla-with-w-values-of-0-identified-as-differentially-abundant/10647 "2019-07-12T09:31:22Z")
**Posts on this page:** 3
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### Author: ![smd](https://forum.qiime2.org/user_avatar/forum.qiime2.org/smd/32/11898_2.png) [@smd](https://forum.qiime2.org/u/smd)
#### Post date: [July 12, 2019, 9:31am UTC](https://forum.qiime2.org/t/ancom-results-phyla-with-w-values-of-0-identified-as-differentially-abundant/10647/1 "2019-07-12T09:31:23Z")

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Hi,  
I'm analyzing a set of samples of COPD patients and Healthy controls, and I've performed ANCOM to assess the differential abundant phyla between the two groups.  
These are the results that I've obtained.  
|k\_\_Bacteria;p\_\_Proteobacteria |3|  
|k\_\_Bacteria;p\_\_Spirochaetes |2|  
|k\_\_Bacteria;p\_\_Firmicutes |1|  
|k\_\_Bacteria;p\_\_Synergistetes |1|  
|k\_\_Bacteria;p\_\_Verrucomicrobia |1|  
|k\_\_Bacteria;p\_\_Actinobacteria |0|  
|k\_\_Bacteria;p\_\_Bacteroidetes |0|  
|k\_\_Bacteria;p\_\_Chloroflexi |0|  
|k\_\_Bacteria;p\_\_Fusobacteria |0|  
|k\_\_Bacteria;p\_\_GN02 |0|  
|k\_\_Bacteria;p\_\_SR1 |0|  
|k\_\_Bacteria;p\_\_TM7 |0|  
|k\_\_Bacteria;p\_\_Tenericutes |0|

 ![image](https://forum-qiime2-org.s3.dualstack.us-west-2.amazonaws.com/original/2X/0/0a1bea3b24357d1adb39c2ff36715b974953fdb7.png)

Can you give me a hint on how to interpret these zero w values?  
thank you in advance  
best regards  
Sara

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### Author: ![jwdebelius](https://forum.qiime2.org/user_avatar/forum.qiime2.org/jwdebelius/32/9655_2.png) [@jwdebelius](https://forum.qiime2.org/u/jwdebelius)
#### Post date: [July 12, 2019, 9:34am UTC](https://forum.qiime2.org/t/ancom-results-phyla-with-w-values-of-0-identified-as-differentially-abundant/10647/2 "2019-07-12T09:34:56Z")

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Hi @smd,

ANCOM looks at the ratio between features as the input for a test, and the W statistic is the number of ratios between that feature and every other that was significantly different. So, an ANCOM W of 0 means that no tests were significantly different.

Your results at the phylum level aren't terribly surprising; Phylum level is a really high level grouping and many people find higher level differences are driven by changes at lower levels (often ASV/OTU or genus).

Best,  
Justine

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### Author: ![system](https://forum-qiime2-org.s3.dualstack.us-west-2.amazonaws.com/original/3X/2/1/21af5fe23cb6f4579467c66a9ed94e55274ca7bd.svg) [@system](https://forum.qiime2.org/u/system)
#### Post date: [August 12, 2019, 3:35pm UTC](https://forum.qiime2.org/t/ancom-results-phyla-with-w-values-of-0-identified-as-differentially-abundant/10647/3 "2019-08-12T15:35:01Z")

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