From: Employing phylogenetic tree shape statistics to resolve the underlying host population structure
Tree statistics | Definition | References |
---|---|---|
Cherry | Pair of leaves that is adjacent to a common ancestor node. | |
Normalized number of cherries | Number of cherries divided by half the number of tips in a tree. | [46] |
Sackin index | Sum of all the number of edges from a leaf to a root for each of a leaf in a tree. | |
Normalized Sackin index | Sackin index divided by \((0.5\times (n(n+1))-1)\), where n is the number of tips. | [46] |
Colless index | Sum of absolute differences between left and right hand leaves (terminal tips) subtended at each internal node of a tree, the root inclusive. | |
Normalized Colless index | Colless index divided by \(\frac{(n-1)(n-2)}{2}\), where n is the number of tips. | [45] |
Total cophenetic index | Sum of all depths of the lowest common ancestor for all pairs of leaves in a tree. | [33] |
Ladder length | Ratio of maximum number of connected internal nodes with a single descendant leaf to number of leaves in a tree. | [25] |
Maximum depth | Maximum number of edges from a leaf to a root for all the leaves in a tree. | [25] |
Maximum width | Maximum number of nodes for each possible depth of a tree. | [25] |
Width-depth ratio | Ratio of maximum width of a tree to its maximum depth. | [25] |