Agenda-manipulation in ranking

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Abstract: A committee ranks a set of alternatives by sequentially voting on pairs, inan order chosen by the committee s chair. Although the chair has no knowledgeof voters preferences, we show that she can do as well as if she had perfectinformation. We characterise strategies with this regret-freeness property intwo ways: (1) they are efficient, and (2) they avoid two intuitive errors. Oneregret-free strategy is a sorting algorithm called insertion sort. We show thatit is characterised by a lexicographic property, and is outcome-equivalent to arecursive variant of the much-studied amendment procedure.