The idea behind LIPEA is to identify specific altered pathways - provided by the KEGG Database - using exclusively lipid compounds. The approach used to this task is the Over Representation Analysis (ORA). ORA starts with considering a list of annotated lipids (e.g. a lipid set related with a signature), then uses the Fisher exact test to verify if the annotations are over represented among a label (pathway) compared to the whole universe of lipids (background), that could be selected as “predefined” for a specific organism (it means, LIPEA will take all the compounds from the pathways related with the selected organism) or be a custom list given by the user.
The steps of the algorithm used to implement the ORA are the following.