TABLE 1. Contingency table for two taxa A and B. Here a is the count of locations where both species A and B occur, b is the count of locations where A occurs but B doesn't, c is the count of locations where B occurs but A doesn't, and d is the count of locations where neither A nor B occur. We denote by n the total number of locations, i.e., n=a+b+c+d. The occurrence of A and B is denoted by A=1 and B=1, and non-occurrence by A=0 and B=0, respectively.

		B=1	B=0
	A=1	a	b
	A=0	c	d