Figure 4.

Peak correlation and peak co-occurrence combined heatmap. The upper-right corner shows the Kendall-tau correlation among consistently assigned lipid features. Strong intra-category correlation is observed for some lipids which possibly results from co-regulation. Shown in the bottom-left is the co-occurrence of consistently assigned lipid features. There are two sub-populations of sterols: one that co-occurs with a sub-population of sphingolipids and another that co-occurs with a sub-population of glycerophospholipids. The biological relevance of this co-occurrence is unclear. Alternatively, this co-occurrence may simply be artifactual, if these lipids were generally of lower relative abundance.