The Taxonomic index of congruence (Ctax and mCtax)

The Ctax allows the comparison of the congruence of taxonomies inferred by two different SD approaches. The Ctax is the ratio of the number of speciation event hypotheses (pairwise species boundaries) congruently supported by the two approaches, relative to the total number of such hypotheses cumulatively supported by them: where A and B represent two different SD approaches, n(A∩B) represent the total number of speciation event hypotheses congruently supported both by A and by B, and n(AUB), the total number of speciation event hypotheses congruently supported by A and/or by B.

Thus, the highest value (Ctax = 1) indicates that both approaches give identical taxonomies, supporting exactly the same species hypotheses (thus suggesting a reduced alpha-error). If the index is low, this indicates incongruence between the SD approaches (underestimation, overestimation, or mis-estimation by at least one of them).

Figure extracted from PLoS One. 2013 Jul 12;8(7):e68242 doi:10.1371/journal.pone.0068242.g001.