Max/min value of enrichment score

Question

[runningonempty]

Hi all,

We've been discussing lately about if the enrichment score (ES), not the normalized (NES), can have values higher that 1 and lower than -1. I've done several tests using fgsea (R, package) and I never get an ES out of the range of the range of [1,-1].

Is it possible to get an ES outside this range? If this is possible, when can an ES be outside this range.

Thanks all for your time.

Answer 1

[alserg]

No, it's not possible. The maximal and minimal ES values are exactly 1 (when the selected genes are exactly the top up-regulated) and -1.

You can check out the section "4.1 Geometric interpretation of GSEA statistic" of fgsea preprint (https://www.biorxiv.org/content/10.1101/060012v1.full) for the better understanding on why it is so.