While market design advocates for the importance of good design to achieve desirable properties, experiments on coalition formation theory have shown fragility in proposed mechanisms to do so. We experimentally investigate the effectiveness of “structured” mechanisms that implement the Shapley value as an ex ante equilibrium outcome with those of corresponding “semi-structured” bargaining procedures. We find a significantly higher frequency of grand coalition formation and higher efficiency in the semi-structured than in the structured procedures regardless of whether they are demand-based or offer-based. While significant differences in the resulting allocations are observed between the two structured procedures, little difference is observed between the two semi-structured procedures. Finally, the possibility of free-form chat induces an equal division more frequently than occurs without it. Our results suggest that when it comes to bargaining and coalition formation, not having various restrictions imposed by different mechanisms may lead to more desirable outcomes.
