We propose a formal concept of the power of voice in the context of a simple model where individuals form groups and trade in competitive markets. Individuals use outside options in two different ways. Actual outside options reflect the possibility to exit or to join other existing groups....

We integrate individual power in groups into general equilibrium models with endogenous group formation. We distinguish between formal power (the say in group decisions) and real power (utility gain from being in groups). Their values will be determined as part of the equilibrium. We find that...