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'''Approval-based primary election methods''' are [[Electoral system|electoral systems]] based in the "[[approval voting]]" single-winner system, but allow for the selection of multiple candidates. They are designed as proposals to replace [[Primary election|primary elections]].
This page lists three sets of rules
* St, Louis method - this is the method adopted by the city of St. Louis for their non-partisan primaries.<ref name=":0">{{Cite web|url=https://stlapproves.org/s/PETITION.pdf|title=PETITION FOR PROPOSITION D|last=STL Approves|first=|date=|website=STL Approves|url-status=live|archive-url=|archive-date=|access-date=}}</ref>
The "St, Louis method" is the only one in use in public elections, as it was adopted by the city of St. Louis for their non-partisan primaries in 2019.<ref name=":0">{{Cite web|url=https://stlapproves.org/s/PETITION.pdf|title=PETITION FOR PROPOSITION D|last=STL Approves|first=|date=|website=STL Approves|url-status=live|archive-url=|archive-date=|access-date=}}</ref>
* "Maximum approval top-two" or "MATT" is an approval-based primary where voters use an [[W:approval voting|approval voting]] ballot to select which candidates would be acceptable to advance to the general election. The maximum approval top-two method then selects no more than two candidates to advance to a general election.
* "Majority approval filter" or "MAF" is an approval-based primary election method that advances all candidates who are approved by a majority of the electorate, as well as often selecting one or more opposition candidates.
== History ==
The rules for the various methods are described below, in order from simplest to most complicated:
{{anchor|STL}}
=== St. Louis method ===
{{anchor|St. Louis method}}
=== Unified primary ===
[[File:STL-sample-ballot-for-2021-03-02-election.png|thumb|Heading from the sample ballot for Heading from sample ballot for the March 2021 primary election in [[St. Louis, Missouri]]<ref>https://www.stlouis-mo.gov/government/departments/board-election-commissioners/documents/upload/Mar2021AllRacesBallot2.pdf</ref><ref>https://www.reddit.com/r/EndFPTP/comments/lfn1sh/sample_approval_voting_ballot_for_the_march_2nd/</ref>
]]{{main|Unified primary}}
]]
The St. Louis method is defined in a short paragraph on the 2020 ballot petition:<ref name=":0" /><blockquote>''Notwithstanding any other provision of law to the contrary, in the primary election for the [offices in question], voters shall select as many candidates as they approve of for each office. The two candidates receiving the most votes for each office shall advance to the general election. The candidate for each office receiving the most votes in the general election shall be declared the winner.''</blockquote>The ballot petition above passed with over 68% of the vote in the [[St. Louis, Missouri|city of St. Louis]] in November 2020.<ref>{{Cite web|last=Schlinkmann|first=Mark|title=Overhaul of St. Louis election system passes, residency rule repeal fails|url=https://www.stltoday.com/news/local/govt-and-politics/overhaul-of-st-louis-election-system-passes-residency-rule-repeal-fails/article_d37f0b73-c0b6-56d7-b093-8d069c314813.html|access-date=2021-02-06|website=STLtoday.com|language=en}}</ref>
The ''unified primary'' method is the method currently used in St. Louis, Missouri, was used in the [[2021 St. Louis mayoral election]], resulting in the election of [[Tishaura Jones]]. This method is defined in a short paragraph on the St. Louis 2020 ballot petition:<ref name=":0" /><blockquote>''Notwithstanding any other provision of law to the contrary, in the primary election for the [offices in question], voters shall select as many candidates as they approve of for each office. The two candidates receiving the most votes for each office shall advance to the general election. The candidate for each office receiving the most votes in the general election shall be declared the winner.''</blockquote>The ballot petition above passed with over 68% of the vote in the [[St. Louis, Missouri|city of St. Louis]] in November 2020.<ref>{{Cite web|last=Schlinkmann|first=Mark|title=Overhaul of St. Louis election system passes, residency rule repeal fails|url=https://www.stltoday.com/news/local/govt-and-politics/overhaul-of-st-louis-election-system-passes-residency-rule-repeal-fails/article_d37f0b73-c0b6-56d7-b093-8d069c314813.html|access-date=2021-02-06|website=STLtoday.com|language=en}}</ref>
{{anchor|MATT}}
=== Maximum approval top-two (MATT) ===
{{main|User:RobLa/MATT}}
"'''Maximum approval top-two'''" (or "MATT") is a voting system that was proposed by [[User:RobLa]], based on discussions that happened on the [[election-methods mailing list]] in 2018.<ref name=":1" /><ref name=":2" />
"''Maximum approval top-two''" (or "''MATT''") is an approval-based primary system where voters use an [[W:approval voting|approval voting]] ballot to select no more than two candidates to advance to the general election. It was proposed by [[User:RobLa]], based on discussions that happened on the [[election-methods mailing list]] in 2018.<ref name=":1" /><ref name=":2" />
[[Category:Approval methods]]
MATT uses the following steps:
[[Category:Approval voting]]
#The candidate who receives the highest approval rating (the "front-runner") qualifies for the general election
#*Example: if there are 100 voters, and 40 approve of "A" and "B", 30 approve of only "B", and 30 approve of only "C", then "B" advances to the general election, since "B" is approved by 70% of voters.
#A second candidate (the "complementary candidate"), who maximizes the approval of the electorate, also qualifies (i.e. by having the highest approval among voters that did ''not'' approve of the front-runner). If two candidates both satisfy an equal part of the remaining electorate, the candidate with the highest overall approval rating advances.
#*Example: if there are 100 voters, and 40 approve of both "A" and "B", 30 approve of only "B", and 30 approve of only "C", then
#**"B" advances with 70% approval (per step 1)
#**"C" advances (per this step). "B" satisfies 70% of the electorate, and "C" satisfies the other 30%. So, 100% of the voters will be satisfied with one of their choices in the general election.
{{anchor|MAF}}
# The candidate who receives the highest approval rating (the "front-runner") qualifies for the general election
===Majority approval filter (MAF)===
#* Example: if there are 100 voters, and 40 approve of "A" and "B", 30 approve of only "B", and 30 approve of only "C", then "B" advances to the general election, since "B" is approved by 70% of voters.
{{main|User:RobLa/MAF}}
# A second candidate (the "complementary candidate"), who maximizes the approval of the electorate, also qualifies (i.e. by having the highest approval among voters that did ''not'' approve of the front-runner). If two candidates both satisfy an equal part of the remaining electorate, the candidate with the highest overall approval rating advances.
#* Example: if there are 100 voters, and 40 approve of both "A" and "B", 30 approve of only "B", and 30 approve of only "C", then
#** "B" advances with 70% approval (per step 1)
#** "C" advances (per this step). "B" satisfies 70% of the electorate, and "C" satisfies the other 30%. So, 100% of the voters will be satisfied with one of their choices in the general election.
[[Category:Approval methods]]
=== Majority approval filter (MAF) ===
Majority approval filter (or "MAF") is another approval-based primary method, mainly devised by [[User:RobLa]] in 2018 (in discussion with Ted Stern and other members of the [[election-methods mailing list]]).<ref name=":1" /> It's a set of rules for holding a primary election with an [[W:Approval Voting|approval Voting]]-style ballot, providing motivation for all candidates to achieve the highest approval rating. The "Ballot Satisfaction Score" is the percentage of the electorate which approves of at least one candidate on a given ballot.
:'''''Draft 4''' published December 28, 2018''
The goal of the system is to provide the least-objectionable approval-based system that would achieve the following:
This set of rules is broken into three parts: 1) The goal of MAF, 2) the definition of "Pools" of candidates advanced to the general election in this system, and 3) the rules for populating the Pools of candidates. It is written with some effort toward legal precision and legal document tools-of-the-trade (e.g. the use of [http://lexicontools.com/defined_term.php capitalized "defined terms"]), but more work is needed.
*Ensures the candidate with the highest approval rating isn't eliminated
* Prefers a second candidate who may not be approved by voters who approved the top candidate, but has a high approval rating, too.
* Prefers selecting two candidates who are approved by over 75% of the electorate, through a set of rules involving a "Ballot Satisfaction Score" and ensuring that at least one of the two advancing candidates are approved by 75%
There are many rules to ensure this outcome. While not as simple as the St. Louis method or MATT, it handles more oddball cases (where an "unjust" outcome may occur) than either of the former two methods.
==== Goal ====
A set of rules for holding a primary election with an [[W:Approval Voting|Approval Voting]]-style ballot, providing motivation for all candidates to achieve the highest approval rating, and resulting in a general election Ballot Satisfaction Score of at least 75%. The "Ballot Satisfaction Score" is the percentage of the electorate which approves of at least one candidate on a given ballot.
==== Pools ==Footnotes==
<references />
Candidates advancing to the general election must qualify for one of the following "Pools". Candidates that don't qualify for one of the Pools below are "Non-advanced Candidates". By default, all candidates are Non-advanced Candidates until they qualify for one of these Pools:
* "Supermajority Candidate Pool" - all candidates who receive greater than 75% approval
* "Plurality Candidate Pool" - all candidates who receive greater than 50% approval, but do not qualify for the Supermajority Candidate Pool. If no candidate receives greater than 50% approval, this pool will contain the leading candidate, who may have less than 50% approval.
* "Opposition Candidate Pool" - a subset of candidates who receive greater than 40% approval, but do not qualify for the Plurality Candidate Pool
[[Category:Approval voting]]
==== Rules ====
[[Category:Primary elections]]
Sequential steps for filling the above Pools with qualified candidates:
[[Category:Multi-winner voting methods]]
# Select the candidate who receives the highest approval rating. This is the "Top Candidate" and automatically qualifies for the general election ballot by one of the following rules:
#* 1a. If the Top Candidate receives greater than 75% approval, add this candidate to the Supermajority Candidate Pool.
#* 1b. If the Top Candidate receives less than 75% approval, add this candidate to the Plurality Candidate Pool.
# Complete the Supermajority Candidate Pool and the Plurality Candidate Pool using the following rules:
#*2a. Add any Non-advanced Candidates with greater than 75% approval to the Supermajority Candidate Pool
#*2b. Add any Non-advanced Candidates with less than 75% approval, but greater than 50% approval to the Plurality Candidate Pool
#Evaluate the Ballot Satisfaction Score (defined above) using the following rules:
#*3a. If the Ballot Satisfaction Score is greater than 75%, candidate selection is complete. Skip to step 6
#*3b. If the Ballot Satisfaction Score is less than 75%, proceed to step 4.
#If there is one or more candidates in the Plurality Candidate Pool, attempt to add an equal number qualified candidates to the Opposition Candidate Pool, evaluating each Non-advanced Candidate using the following steps
#*4a. Find the Non-advanced Candidate with the highest approval score.
#**If this candidate has less than 40% approval, determine if this candidate qualifies for the Opposition Candidate Pool in step 5.
#**If this candidate has greater than 40% approval, add this candidate to the Opposition Candidate Pool, then proceed to step 4b.
#*4b. Compare the size of the Plurality Candidate Pool and the Opposition Candidate Pool
#**If the Plurality Candidate Pool has more candidates than the Opposition Candidate Pool, skip back to step 3.
#**If the Opposition Candidate Pool contains an equal number of candidates to the Plurality Candidate Pool, proceed to step 5.
# If the Ballot Satisfaction Score is greater than 50%, skip to step 6. If the Ballot Satisfaction Score is under 50%, ensure at least two candidates advance to the general election using the following steps:
#*5a. If there are no candidates in the Opposition Candidate Pool, find the Non-advanced Candidate with the highest approval score. If this candidate increases the Ballot Satisfaction Score by more than 10% (the "Candidate Differentiation Threshold"), add this candidate to the Opposition Candidate Pool, and skip to step 6. Otherwise, advanced to step 5b.
#*5b. Consider each Non-advanced Candidate in order of approval score. Find the first candidate who increases the Ballot Satisfaction Score by more than the Candidate Differentiation Threshold (10%), and add this candidate to the Opposition Candidate Pool, and skip to step 6. Otherwise, advance to step 5c.
#*5c. Find the Non-advanced Candidate with the highest approval rating. Add this candidate to the Opposition Candidate Pool, and advance to step 6.
# Candidate selection is complete. Advance all candidates in the Supermajority Candidate Pool, the Plurality Candidate Pool, and the Opposition Candidate Pool to the general election.
==History==
* MAF (note: Full discussion history of this method can be found at [[Talk:Majority approval filter]])
** 2018-12-28 - Draft 4 published at <https://electowiki.org/wiki/MAF>, based on conversation documented at [[Talk:Majority approval filter]])
** 2018-12-07 - [https://electowiki.org/w/index.php?title=Majority_approval_filter&oldid=5200 Draft 3] published (with clarifying edits continuing through 2018-12-10). See December email thread "[http://lists.electorama.com/pipermail/election-methods-electorama.com/2018-December/thread.html <nowiki>[EM] Approval-based replacement for jungle primary</nowiki>]" for more discussion about the evolution of this draft
**2018-11-22 - Draft 2 published in [http://lists.electorama.com/pipermail/election-methods-electorama.com/2018-November/001925.html 2018-11-22 email from RobLa] (and also available at [[User:RobLa/MAF drafts#Draft 2]]
**2018-11-20 - first draft published on electowiki.org and as "[https://medium.com/@robla/replacing-the-jungle-primary-c1e844a5333b Replacing the jungle primary]" by [[User:RobLa]] (and also available at [[User:RobLa/MAF drafts#Draft 1]])
*MATT: Full discussion history of this method and it's counterpart ([[Majority approval filter]]) can be found at [[Talk:Majority approval filter]])
**2018-11-20 - first draft published on electowiki.org and as "[https://medium.com/@robla/replacing-the-jungle-primary-c1e844a5333b Replacing the jungle primary]" by [[User:RobLa]]
* [[Majority approval filter]] (MAF; [https://electowiki.org/w/index.php?title=User:RobLa/Approval-based_primary_election_methods&action=history history of the page formerly known as "MAF"]) - a primary election voting method that is guaranteed to advance all candidates receiving a majority approval score to the general election
* [[Maximum approval top-two]] (MATT; [https://electowiki.org/w/index.php?title=Maximum_approval_top-two&action=history page history for MATT]) - a simplification of MAF that is guaranteed to advance no more than two candidates.
[[Category:Approval methods]]
== Footnotes ==
<references />
[[Category:Approval methods]]
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