The Relative Taxonomic Resolving Power Index (Rtax)
The Rtax quantifies the ability of a given SD approach to reveal a high number of potential candidate species, relatively to other approaches. Of the complete set of speciation event hypotheses cumulatively suggested by all approaches, the proportion supported by a given approach becomes its Rtax: for an example with four approaches to be compared (A, B, C, D) with n(AUBUCUD) being the total number of possible speciation events revealed (i.e. supported by A and/or B and/or C and/or D).
High values indicate high relative resolving power of a SD approach, but do not necessarily imply reliability of the results: a high Rtax indicates that an approach can alone retrieve all the species boundaries that have been independently identified by all the approaches, meaning a minimization of the beta-error (false negatives), but possibly a maximization of the alpha-error (false positives).
Figure extracted from PLoS One. 2013 Jul 12;8(7):e68242 doi:10.1371/journal.pone.0068242.g001.