Quartet Distance

The quartet distance is a way of measuring the distance between two unrooted phylogenetic trees on the same set of leaves, computed as the number of subsets of four leaves whose induced topology differs between the two trees. A direct computation takes time proportional to the fourth power of the number of leaves, but faster algorithms exist for binary trees, with running times close to linear in the number of leaves, and an algorithm exists for trees whose internal nodes may have more than two children. The measure is used in computational phylogenetics and bioinformatics to compare and evaluate reconstructed evolutionary trees, and implementations exist in C, Perl and R. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/