Can relative abudance be more than 100?

[Zeynel]

I'm looking at my American Gut results. The last column shows the relative abundance of bacteria.

#taxon                                                                                                                                     relative_abundance
k__Bacteria;p__Bacteroidetes;c__Bacteroidia;o__Bacteroidales;f__Bacteroidaceae;g__Bacteroides    487.453
k__Bacteria;p__Firmicutes;c__Clostridia;o__Clostridiales;f__Lachnospiraceae;g__    133.097
k__Bacteria;p__Verrucomicrobia;c__Verrucomicrobiae;o__Verrucomicrobiales;f__Verrucomicrobiaceae;g__Akkermansia    69.620

According to this table, relative abundance of Bacteroids is 487.453. I read this as "487.453 per cent". But this does not make sense to me because, relative abundance is described as "the number of organisms of a particular kind as a percentage of the total number of organisms of a given area or community". If so, relative abundance should be less than hundred. Can you explain where I err? Thanks.

 

[jim mcnamara]

A definition of relative abundance is:

the number of organisms of a particular kind as a percentage of the total number of organisms of a given area or community;
the number of birds of a particular species as a percentage of the total bird population of a given area

So that figure, for whatever reason, is not a percentage, by definition: percentages have values between 0 and one multiplied by 100.

So something else is going on. Did the American Gut project people not give you explanatory material? Read that very carefully.

 

[jim mcnamara]

I just read the website - I think it might be an estimate the number of different organisms (species) from that Phylum, not a percentage. Someone involved with the study could certainly get us both on the right path.

 

[Ygggdrasil]

Relative abundance does not necessarily imply percentage. It's useful to think of relative abundance in contrast to its alternative absolute abundance. Absolute abundance tells you the exact number of each species present in your sample. Relative abundance just means that you don't know the total number, but you do know the relative proportion of bacteria in your sample (e.g. you have roughly 2 bacteria of species A for every bacteria of species B).

Anyway, it's trival to convert the data to percentages.

 

[Zeynel]

Sorry, this was my mistake. They had three links for the results and all said "Summary" and I assumed all were in the same format. I will ask American Gut and post here what those numbers represent. Sorry again for the confusion.