The variance of leaf depth statistic returns the variance of depths across all tips.
var_leaf_depth(phy, normalization = "none")
Variance of leaf depths
phylo object or ltable
"none" or "yule", when "yule" is chosen, the statistic is divided by the Yule expectation
T. M. Coronado, A. Mir, F. Rosselló, and L. Rotger. On Sackin's original proposal: the variance of the leaves' depths as a phylogenetic balance index. BMC Bioinformatics, 21(1), 2020. doi: 10.1186/s12859-020-3405-1.