Youden's J statistic

The index was suggested by W. J. Youden in 1950[1] as a way of summarising the performance of a diagnostic test; however, the formula was earlier published in Science by C. S. Peirce in 1884.

The index is represented graphically as the height above the chance line, and it is also equivalent to the area under the curve subtended by a single operating point.

Youden's J, Informedness, Recall, Precision and F-score are intrinsically undirectional, aiming to assess the deductive effectiveness of predictions in the direction proposed by a rule, theory or classifier.

DeltaP is Youden's J used to assess the reverse or abductive direction,[4][7] (and generalizes to the multiclass case as Markedness), matching well human learning of associations; rules and, superstitions as we model possible causation;,[5] while correlation and kappa evaluate bidirectionally.

[5] The main article on Matthews correlation coefficient discusses two different generalizations to the multiclass case, one being the analogous geometric mean of Informedness and Markedness.