The enrichment score (ES) is the main output of GSEA. It represents the number of genes in the gene set that are over-represented at the extremes on the ranked list (most up or down regulated).
- The ES is the maximum deviation from zero, encountered during the random walk that goes through the ranked list.
- Higher the ES score, it more likely for a gene set to shift towards either end of the ranked list.
For more details, please refer to the original documentation from GSEA.