Fresh SI: Okada & Sawa on the implications of collective agency arising from majority voting

In a new working paper, Akira Okada and Ryoji Sawa examine an evolutionary model in which the policy followed by a collective is determined by majority (or supermajority) voting by individuals. They look at the kind of policies that emerge under given voting rules.

A voting rule can be considered a way of forming a collective intention. In fact, it can be a strong way of forming a collective intention as the wishes of individuals in a minority are disregarded. It follows that, in this sense, the weakest voting rule is the one that requires ALL individuals to agree: the unanimity voting rule.

Under the unanimity rule, the only way a new policy x can defeat a status quo policy y is if every individual voting weakly prefers x to y. This is exactly the Coalitional Better Response rule found in Newton and Angus (2015, paper, video).

Okada and Sawa find that when their voting dynamic is perturbed uniformly, in the long run Condorcet winning  policies tend to emerge. When perturbations depend on payoffs (specifically, logit) Borda winning policies tend to emerge.

For more, see the paper.