Could an enrichment factor be calculated and make sense for metagenomic data?

Question

[arronar]

Hello.

I was talking with a friend of mine last days analyzing a distribution graph that I show to him and looks like the following.

To produce it, I just shorted all the samples of a specific run according to their abundance and got it.

The question we had was if we can somehow calculate an enrichment factor.

So if for each sample we know it's origin and by this I mean where did it come from (e.g soil, water, food, etc) is it a valid question to ask "How enriched this distribution is for each origin / what is the enrichment of each origin"?

Is it valid or in order to calculate some kind of enrichment you have to have a control/distribution/prior knowledge ?

Any ideas/hints/help are welcome.