Using experiments to compare the predictive power of models of multilateral negotiations

We conduct unstructured negotiations in a laboratory experiment designed to empirically assess the predictive power of models of the multilateral negotiations observed in diverse strategic settings. For concreteness we consider two sellers negotiating with a buyer who wants to make only one trade, and we categorize the models by whether introducing a second seller to bilateral negotiations always, never, or sometimes increases the buyer's payoff. Our experiment features two scenarios within which the three categories of models have observationally distinct predictions: a differentiated scenario with one high-surplus seller and one low-surplus seller, and a homogeneous scenario with identical high-surplus sellers. In both scenarios the buyer tends to trade with a high-surplus seller at terms indistinguishable from those in bilateral negotiations with a high-surplus seller, meaning that introducing a competing seller does not substantially affect the observed terms of trade. Our findings match the predictions from models in the never-matters category, supporting their use when modeling multilateral negotiations.