Candidate cloning – executive summary

  1. If a second candidate A, almost identical to B in the eyes of all voters, enters the race (or withdraws) that should neither hurt nor help B's chances of being elected (aside from replacement by a clone). More precisely: "clones" in rank-order-ballot systems all are ranked adjacent by every voter. In ratings-type systems they are all rated within ±ε by every voter in the limit ε→0.
  2. But Plurality, Borda, and Copeland voting all hugely-fail this test. That makes election manipulation easy (plus often more cost-effective than "running an honest race").
  3. Range and Instant Runoff voting both pass this test ("cloneproof").

Fuller candidate-cloning page

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