The institutional effect on majority rule instability: Bicameralism in spatial policy decisions

the constitutional requirement that legislation must be approved by a majority of two chambers increases the likelihood that: a core will exist, even in situations in which a core would not exist under a unicameral majority rule. Laboratory experiments were run on forty six-person groups. with constant induced preferences in a two-dimensional policy space. Groups were assigned to one of four treatments. in three treatments, members were assigned to two three-person chambers, and a majority of each chamber was required to make policy decisions. In two of these treatments, the assignment induced a bicameral core; in one it did not. The fourth, a control treatment, was a unicameral, simple majority-rule game with no core. The variance in each of the two cases with a bicameral core was significantly less than in the no-core bicameral or the unicameral treatments. in the cases with a bicameral core,the outcomes clustered closely around the predicted core outcomes. The results provide strong support for the stability-inducing properties of bicameralism and for the core as a predictor of this effect. Players received statistically greater rewards in those treatments in which their role was pivotal in achieving the core.