The impossibility of unbiased judgment aggregation


Συγγραφέας: Franz Dietrich, Christian List


Franz Dietrich, Christian List: The impossibility of unbiased judgment aggregation (pdf, 20 pages)
Standard impossibility theorems on judgment aggregation over logically connected propositions either use a controversial systematicity condition or apply only to agendas of propositions with rich logical connections. Are there any serious impossibilities without these restrictions? We prove an impossibility theorem without requiring systematicity that applies to most standard agendas: Every judgment aggregation function (with rational inputs and outputs) satisfying a condition called unbiasedness is dictatorial (or e¤ectively dictatorial if we remove one of the agenda conditions). Our agenda conditions are tight. Applied illustratively to (strict) preference aggregation represented in our model, the result implies that every unbiased social welfare function with universal domain is e¤ectively dictatorial. Keywords: judgment aggregation, logic, impossibility, May’s neutrality...