The Match Ratio, is also intended to assess the agreement between two alternative partitions. In contrast with the Ctax, this index is based on similarity (number of identical subsets), relative to the total number of subsets delimited by both SD approaches):
where n match is the number of subsets congruently delimited by two approaches A and B (identical content), and nA and nB are the number of subsets delimited by A and by B.
Ahrens D., Fujisawa T., Krammer H.J., Eberle J., Fabrizi S., Vogler A.P. 2016. Rarity and Incomplete Sampling in DNA-Based Species Delimitation. Syst. Biol. 65(3):478–494.