Obvious Independence of Clones

Ratip Emin Berker, Sílvia Casacuberta, Christopher Ong, Isaac Robinson

Abstract: The Independence of Clones (IoC) criterion for social choice functions (voting rules) measures a function's robustness to strategic nomination. However, prior literature has established empirically that individuals cannot always recognize whether or not a mechanism is strategy-proof and may still submit costly, distortionary misreports even in strategy-proof settings. The intersection of these issues motivates the search for mechanisms which are Obviously Independent of Clones (OIoC): where strategic nomination or strategic exiting of clones obviously have no effect on the outcome of the election. We examine three IoC ranked-choice voting mechanisms and the pre-existing proofs that they are independent of clones: Single Transferable Vote (STV), Ranked Pairs, and the Schulze method. We construct a formal definition of a voting system being Obviously Independent of Clones based on a reduction to a clocked election by considering a bounded agent. Finally, we show that STV and Ranked Pairs are OIoC, whereas we prove an impossibility result for the Schulze method showing that this voting system is not OIoC.