I prove that under each strategy-proof and unanimous social choice correspondence, there is at least one agent who is decisive. Because the result is established on a weak requirement on preferences over sets, the existence of a decisive agent is an underlying feature of most strategy-proof and...

I consider whether the agentsʼ reluctance to make a large lie is helpful for the rule designer to construct a nonmanipulable rule. For this purpose, I study an axiom, called AM-proofness, saying that manipulation cannot occur through preferences adjacent to the sincere one. Through examples, I...

A social welfare function satisfies Bounded Response if the smallest change in the variable (i.e., preference profile) leads to the smallest change, if any, in the value (i.e., social preference). We show that each social welfare function on each connected domain satisfies Bounded Response and a...

The required amount of information to make a social choice is the cost of information processing, and it is a practically important feature of social choice rules. We introduce informational aspects into the analysis of social choice rules and prove that (i) if an anonymous, neutral, and...

There are many situations where the indifference classes of the agents' preferences are exogenously given. We present a framework for dealing with such situations and find that the cardinality of the set S, which consists of alternatives that every agent ranks strictly, is critical to the...

I correct the statements of Theorems 3.1 and 3.2 and the proof of Theorem 3.1 in Sato (Informational requirements of social choice rules, Mathematical Social Sciences 57 (2009) 188-198). I add a condition requiring that each rule in the theorems does not choose the entire set of the alternatives...