Approval voting is a single-winner electoral system where each voter may select ("approve") any number of candidates. The winner is the most-approved candidate.

On paper, approval voting seems like an excellent system:

  • It is easy to explain
  • You can use the same voting machines and ballots
  • It never requires more than one round of voting
  • It avoids spoilers and reduces the opportunity for strategic voting
  • It encourages candidates to be more centric in their policies

So why isn't approval voting used more often in elections?

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    Could you possibly explain your definition of it? I mean, it is easy to explain. – hszmv May 31 '18 at 15:10
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    “reduces the opportunity for strategic voting” – [citation needed] – chirlu May 31 '18 at 18:29
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    "You can use the same ballots" But you probably shouldn't. Having explicit "Approve" and "Disapprove" next to each candidate makes the ballots resistant to tampering, and also makes it clear that one-person-one-vote still applies. (Every voter votes for or against every candidate.) – endolith Jun 1 '18 at 14:24
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    @endolith: All deterministic voting systems. – origimbo Jun 2 '18 at 0:58
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    @origimbo All practical voting systems, then. :) – endolith Jun 2 '18 at 20:14

Approval voting does not meet the following criteria:

  • Majority: if a majority of voters prefer one candidate to every other candidate, does that candidate win?
  • Majority loser: if a majority of voters prefer every other candidate over one candidate, does that candidate lose?
  • Mutual majority: if a majority of voters prefer every member of a group of candidates to all candidates not in the group, does a member of that group win?
  • Condorcet: if there is a unique Condorcet winner, does that candidate win?
  • Condorcet loser: are Condorcet losers guaranteed to lose?
  • Smith and ISDA.
  • Later no harm. If I add a candidate to my ballot, is that guaranteed not to make a more favored ballot lose?

Later-no-harm and Condorcet are incompatible, so no voting method supports both. But many voting methods manage one or the other.

You can use the same voting machines and ballots

Ballots sure. I'm not convinced on voting machines. But I'm also not convinced that using the same ballots is a good idea. What if people don't realize that they are supposed to change how they vote and only approve one candidate. Then it devolves into plurality voting.

It never requires more than one round of voting

But that means that voters are choosing among a large number of similar alternatives. Two rounds of voting mean that people who don't know who to choose in the first round can still participate in the second.

It avoids spoilers and reduces the opportunity for strategic voting

It fails later-no-harm, so there are spoilers and strategic voting.

The suggested way to do approval voting is to either order all of the candidates and pick those you prefer more than you wish to avoid or to pick a pivot and compare the rest to that person. If you're ordering all the candidates, you might as well do ranked voting. And choosing a pivot is definitely strategy.

The biggest problem that I have with it is that it doesn't allow me to say that I prefer one candidate to another except in the approval. So I can basically say that I prefer one group of candidates to another group. But I only get two groups. I would rather use one of the more complicated ranked voting methods as better expressing my actual preferences.

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    Some (all?) of these criteria only make sense in the context of ranked ballots, which Approval is not. Applying ranked criteria to non-ranked systems requires you to make assumptions about what's going on inside voters' heads, which is controversial. See Majority criterion:Approval voting, for example. – endolith Jun 1 '18 at 13:58
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    Also, these criteria presume that a majority getting their way at the expense of a minority is a good thing, while advocates of cardinal voting systems believe the opposite (see Peter Emerson's books on how majoritarianism causes war, for instance). Anyway, I doubt any of these academic reasons are why it's "not used more often", which has more to do with unfamiliarity among the population. – endolith Jun 1 '18 at 14:00
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    @endolith all voting uses some simplification based on assumptions of how people think or mater to arrive at a group opinion. So far as I know there is no science to say how much error there is in any theory of thinking, so all systems are backed only by argument; do you like the kinds of fairness X system offers? This answer shows some well regarded fairnesses this system does not offer. I'm also pretty sure these aren't actually closely related to why laws haven't changed, but I think it is very useful information to anyone interested in the idea. – user9389 Jun 1 '18 at 14:53
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    @notstoreboughtdirt I'm specifically talking about these ranked-ballot mathematical criteria, though, and the assumptions you need to make in order to shoehorn a non-ranked system into them. (For instance, "The candidate who received the most votes was not the legitimate winner because, in their heads, a majority preferred someone else.") These assumptions are subjective, not objective, so it's not cut-and-dry whether these voting systems meet these criteria. (And these criteria aren't objectively good, anyway.) – endolith Jun 1 '18 at 16:10
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    @Relaxed Or people have ratings in their heads, which are "flattened" into preferences when using ranked ballots, etc. "The majority judgement experiment proves that the model on which the theory of social choice and voting is based is simply not true: voters do not have preference lists of candidates in their minds. Moreover, forcing voters to establish preference lists only leads to inconsistencies, impossibilities and incompatibilities." hal.archives-ouvertes.fr/hal-00243076/document – endolith Jun 2 '18 at 20:10

Don't discount the weight of history. The generic answer to a closely related question, "why is voting system X used in this election" is frequently that the voting system is picked by the winner, and the winner likes system X because he or she just won under it. Approval voting was only formalized relatively recently, so it hasn't had long to become a favoured system.

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Probably the biggest reason in the US is just unfamiliarity; people are used to thinking in terms of binary Us-vs-Them (elections, sports tournaments, etc.) so the concept that there could be other candidates that are not as divisive, but more acceptable overall, is foreign. We're used to the majoritarian concept of trying to beat the other guys into submission, rather than trying to find a consensus/compromise that we're all ok with.

The biggest psychological problem with Approval voting is that it's not as expressive as other systems. A candidate that you really love and a candidate that you merely find tolerable both get an equal, full-strength vote from you. Ranked and rated systems both allow more expression of preferences.

Probably because of this, in elections that have used Approval, most voters only voted for their favorite candidate, treating it like a FPTP election.1 2 Some places that previously used it repealed it for this reason.

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It encourages candidates to be more centric in their policies

This is not a reason for, this is a reason against. Selling a voting system as skewing the vote plays well with very few people.

Another reason is because your actually voting for 'least disliked' rather than someone that anyone wants,so who is actually going to support the proposal? You're selling a negative.

Yet another reason is, unless there is very strong reasoning, people do not change existing stable systems.

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It is worth pointing out that there are people trying to make a strong case for using approval voting much more broadly, see, e.g., this book: https://www.springer.com/us/book/9780387498959 by Brams and Fishburn. They at least would probably argue that it's not for any fundamentally good reason that it is not being used, rather just due to a combination of historical accident and lack of insight. Of course, others will disagree.

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Australia (and possible New Zealand... it was a Kiwi who introduced me to the concept) does have Instant Run-Off Voting which sounds like this. The basic idea is that if you have five candidates A, B, C, D, E. You can rate them in 3, 2 4, [n], 1 indicating the order of preference for candidates you want.

The results are tallied and the lowest scoring candidate is then eliminated and votes for said candidate are redistributed to the next available candidate on the list until one candidate has 51% of the vote. So if E was the lowest my vote would go B, then A, then D. the [n] is to represent that I absolutely cannot stand Candidate D and would never elect that way so he was never rated. I do not want D (sorry for the pun).

The problem is... well... get a good read on the Australian election system cause it is some bizarre voting regulations... essentially it is not unheard of for Aussie to have a general election ballad that has upwards of 100 candidates for one open seat that only one will win (you don't have to mark all in order, may will just go down the party preference list and order them that way).

The downside of this system is that until the introduction of computer counting machines, this system required several recounts that extended the knowledge gap between election night and the concession speech.

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    Instant Runoff Voting /the Alternative Vote has concepts of ordered preference and of round voting which approval voting lacks, which modifies the selection of traits it might be nice for a voting system to satisfy which the two systems meet. – origimbo May 31 '18 at 19:40

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