1. A computer-implemented method of determining a clustering metric, the method comprising: receiving, by a processor, a first set of transactions; receiving a second set of transactions; and for transaction i of the first set of transactions and transaction j of the second set of transactions: (a) determining an intersection set consisting of transactions that are neighbors of both transaction i and transaction }; (b) determining a union set consisting of transactions that are neighbors of either transaction i or transaction j; (c) computing a common linkage between transaction i and transaction j equal to the intersection set divided by the union set; (d) incrementing index j and repeating steps (a)-(c); (e) summing the common linkages between transaction i and the transactions of the second set of transactions; (f) normalizing the sum of the common linkages by a number of the second set of transactions; (g) incrementing index i and repeating steps (a)-(f); (h) summing the normalized common linkages between the first set of transactions and the second set of transactions; and (i) normalizing the sum of the normalized common linkages by a number of the first set of transactions to determine the clustering metric; and storing the clustering metric in memory.