  Tree congruence metrics are typically global indices that describe the
similarity or dissimilarity between dendrograms. This study principally focuses
on topological congruence metrics that quantify similarity between two
dendrograms and can give a normalised score between 0 and 1. Specifically, this
article describes and tests two metrics the Clade Retention Index (CRI) and the
MASTxCF which is derived from the combined information available from a maximum
agreement subtree and a strict consensus. The two metrics were developed to
study differences between evolutionary trees, but their applications are
multidisciplinary and can be used on hierarchical cluster diagrams derived from
analyses in science, technology, maths or social sciences disciplines. A
comprehensive, but non-exhaustive review of other tree congruence metrics is
provided and nine metrics are further analysed. 1,620 pairwise analyses of
simulated dendrograms (which could be derived from any type of analysis) were
conducted and are compared in Pac-man piechart matrices. Kendalls tau-b is used
to demonstrate the concordance of the different metrics and Spearmans rho
ranked correlations are used to support these findings. The results support the
use of the CRI and MASTxCF as part of a suite of metrics, but it is recommended
that permutation metrics such as SPR distances and weighted metrics are
disregarded for the specific purpose of measuring similarity.
