Trade associations and collusion among many agents: evidence from physicians

We study a recent case where most gynecologists in one city formed a trade association to bargain for better rates with insurance companies. After unsuccessful negotiations, the physicians jointly terminated their insurer contracts and set a minimum price. We find that subsequent realized prices coincided with Nash-Bertrand prices, and that the minimum price was barely binding. We show that these actions ensured the association's stability and increased profits. Our findings shed light on the role of trade association in collusion among a large number of heterogeneous agents, and provide insights for the antitrust analysis of trade associations.