The approval cutoff or neutral preference level is an option that may be used with a ranked ballot.
Specifying a neutral preference level indicates that candidates above a certain rank have positive preference, while candidates below that rank have negative preference. Positive preference is equivalent to an approval vote, while negative preference receives no approval vote. Sometimes candidates at the approval cutoff (also called an approval threshold) are also considered approved, instead of being treated neutrally.
When a method uses a ranked ballot with approval cutoff, the usual procedure is that the neutral preference level is set below all ranked candidates, and above unranked candidates.
A voter can set the approval cutoff above the default level by ranking an extra "Neutral Preference" candidate.
A voter may decide to set the neutral preference level between some ranked candidates in order to indicate that
- among the non-approved candidates, some are more preferred than others.
- the ranking of candidates above and below the line is not as important as having a candidate above the line defeat all candidates below the line.
It is also possible to consider fractional approval thresholds i.e. one threshold which gives candidates 100% approval, a second threshold that gives them 90%, etc. Thesr thresholds would be consecutive, so for example, a voter giving their 2nd choice 100% approval but their 4th choice 90% approval would also give their 3rd choice 90% approval. This would allow the collection of rated ballot information.
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The logic of the approval threshold is that if a voter approves a candidate, and they prefer some other candidate(s) over the candidate they approved, then it's very likely that voter would also approve of those more-preferred candidates if voting with an Approval ballot, since otherwise they'd be giving more support to a candidate they prefer less than the candidates they'd be disapproving.
The preference-approval concept is highly related.
An approval threshold can be used in the context of rated methods as well. This can be useful for cardinal PR, since it could be possible to allow, for example, a Green Party voter to approve both Green Party candidates and Democratic candidates, using the approvals to ensure one of those preferred candidates wins, and then score the candidates in such a way as to maximize the odds that of the preferred candidates, one of the Green Party candidates wins.