Normal distribution needed for perfoming Ancom/Aldex2?

Hello everyone,

My question is if is necessary to check normal distribution for perfoming Ancom or Aldex2 in metagenomic data, that is, a table of relative abundances of microbial species obtained by 16s or shotgun sequencing. As far as I know, ALDEx2 performs Welch’s t-test that requires normal distribution.

And in case it is necessary to check that distribution, with what free program can it be done easily?

Thanks in advance,

Lucia

Hi @LuciaGG,

The short answer is no. The compositional assumption and transformation under Aldex2 is more important than the assumption of normality.

Under the hood, Aldex2 uses a specific data transform with an underlying monte carlo simulation to achieve that transformation. Som if you wanted to test normality, you would need to approach the transformed data.

Best,
Justine

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@jwdebelius Thank you for your kind answer.
Could you please tell if is the same situation for ancom?

Hi @LuciaGG,

I think ANCOM in QIIME 2 uses a kruskal wallis test under the hood. But again, the issues of compositionally trump the issue of normality.

Best,
Justine

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