Collusion, Profits, and Rational Antitrust
Empirical study of cartels, their operations, and their adaptation to legal prohibition, is inherently complicated. Because cartels are unlawful, they operate surreptitiously. We can have no really confident idea how significant or widespread price fixing may be. Asking how many unlawful cartel there are is very much like asking how many miles of unexplored caves there are. Because we are in a position to study only those cartels that we can discover, there may be a significant selection bias in any empirical study cartels.
Collusion, Profits, and Rational Antitrust” (with Robert D. Tollison), Antitrust Bulletin 43 (Summer 1998), pp. 365–374.