A method of determining a clustering metric includes receiving a first set of transactions and a second set of transactions. For transaction i of the first set and transaction j of the second set, the method includes (a) determining an intersection set, (b) determining a union set; (c) computing a common linkage between transaction i and transaction j equal to the intersection set divided by the union set, and (d) incrementing index j and repeating steps (a)-(c). The method also includes (e) summing the common linkages between transaction i and the transactions of the second set, (f) normalizing the sum of the common linkages by a number of the second set, and (g) incrementing index i and repeating steps (a)-(f). The method further includes (h) summing the normalized common linkages and (i) normalizing the sum of the normalized common linkages by a number of the first set.