Strategy-proofness of the unanimity with status-quo rule over restricted domains

Journal: Economics Letters

Social choice theory is the analysis of combining individual opinions, preferences, interests, or welfares to reach a collective decision. To reach a consensus, the social planner chooses a rule (social choice function) which assigns one outcome from a set of total feasible alternatives for every possible combination of individual preferences over these alternatives. One of the main objectives of the planner is to construct rules which incentivize voters to reveal their preferences honestly, i.e. no agent can manipulate the rule. This is called the axiom of strategy-proofness.

In this paper, the researchers consider an interesting social choice function, the Unanimity with Status-quo (U-S) rule. The U-S rule is defined as follows. It identifies an alternative as the status-quo alternative. Whenever an alternative is ranked first by all agents, it selects that alternative. Otherwise, it selects the status-quo alternative. Examples of the U-S rule are as follows. A unanimous consent over one policy out of several policies among countries or organizations is required to come to a mutual agreement. The status-quo outcome is no agreement. These agreements can be on climate change, peace, trade, etc.

The main contribution of the paper is to provide a complete characterization of the preferences of agents over which the U-S rule is strategy-proof. Further, the researchers introduce a notion of “conflicting preferences”. We show that the U-S rule defined over these preferences is strategy-proof.