I'm wondering where the following "normalized relative probability distance function" (for lack of a better name) was first studied: $$d(A,B) = \mathbb P(\overline A\cup\overline B\mid A\cup B)$$ where $\overline A$ is the complement of $A$.

Googling for "distance between events probability" I found it in Goodman, Mathematics of Data Fusion, 1997, but surely that's not the first occurrence.