Why does the Numreads have decimals?

[powerfulDie]

Thank you for this good tool.
I am curious why there are decimals for NumReads. how to explain this?

Any help would be appreciated.

[freekvh]

From https://salmon.readthedocs.io/en/latest/file_formats.html:

NumReads — This is salmon’s estimate of the number of reads mapping to each transcript that was quantified. It is an “estimate” insofar as it is the expected number of reads that have originated from each transcript given the structure of the uniquely mapping and multi-mapping reads and the relative abundance estimates for each transcript.

If you look into how Salmon works, you'll see it's not counting reads, it does "pseudo-alignment" combined with expectation-maximization algorithm for transcript quantification.

I don't understand the details, but I do understand that it is not as simple as counting the reads per transcript. Salmon also optionally translates the transcript abundances to "gene expression" values, all of this will not lead to ints.