[EM] COWPEA and COWPEA Lottery paper on arXiv

Toby Pereira tdp201b at yahoo.co.uk
Fri May 19 04:56:09 PDT 2023

I don't know how many of you will be interested in this, but I wrote a paper on the COWPEA and COWPEA Lottery voting methods, which is now available on arXiv here: https://arxiv.org/abs/2305.08857 They're also described on the wiki: https://electowiki.org/wiki/COWPEA
Basically COWPEA is a proportional approval method that elects candidates with different weights to the elected body. COWPEA Lottery elects a fixed number of candidates with equal weight, but it is non-deterministic. The weight a candidate gets in the elected body under COWPEA is the same as its probability of being elected in the following lottery:
Start with a list of all candidates. Pick a ballot at random and remove from the list all candidates not approved on this ballot. Pick another ballot at random, and continue with this process until one candidate is left. Elect this candidate. If the number of candidates ever goes from >1 to 0 in one go, ignore that ballot and continue. If any tie cannot be broken, then elect the tied candidates with equal probability.

COWPEA Lottery just runs this lottery a fixed number of times to elect the candidates. I see these methods as of theoretical interest because of their criterion compliance. As well as being proportional, they are strongly monotonic, and pass Independence of Irrelevant Ballots. COWPEA Lottery also passes Independence of Universally Approved Candidates (this criterion isn't applicable to COWPEA), and as far as I understand, it is the only method that has been shown to pass all of these criteria.

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