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hare_voting_procedure [2007/10/15 06:33]
jtkorb created
hare_voting_procedure [2009/02/09 15:07] (current)
jtkorb
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 ====== Hare Voting Procedure ====== ====== Hare Voting Procedure ======
  
-The [[http://​sof.uchicago.edu/​hare|Hare System of Proportional Representation]] ​(also described as the [[http://​en.wikipedia.org/​wiki/​Hare_quota Hare Quota]]) ​is a variant ​of the [[http://​en.wikipedia.org/​wiki/​Single_transferable_vote|Single Transferable Vote (STV)]] preferential voting system. ​ It is "​preferential"​ in the sense that voters rank the order of their chosen candidates (using, say, numbers 1-5), rather than using an unranked mark (e.g., one or more "​X"​s). ​ A common application is in the selection of committees, in which multiple winners must be chosen from a set of available candidates.+The [[http://​sof.uchicago.edu/​hare|Hare System of Proportional Representation]] is a procedural description ​of the [[http://​en.wikipedia.org/​wiki/​Single_transferable_vote|Single Transferable Vote (STV)]] preferential voting system. ​ It is "​preferential"​ in the sense that voters rank the order of their chosen candidates (using, say, numbers 1-5), rather than using an unranked mark (e.g., one or more "​X"​s). ​ A common application is in the selection of committees, in which multiple winners must be chosen from a set of available candidates. ​  
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 +(Note: The quota calculation described in this document and used in the associated software is actually based on the [[http://​en.wikipedia.org/​wiki/​Droop_quota|Droop Quota]], not the [[http://​en.wikipedia.org/​wiki/​Hare_quota|Hare Quota]]. ​ The term //Hare// is retained here as the common name for //Single Transferable Vote// despite this inaccurate characterization.)
  
 ====== Background ====== ====== Background ======
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 The procedure used by the College of Science is described in this [[http://​www.science.purdue.edu/​faculty_staff/​policies/​PP2006_11_16.pdf|document]],​ starting at page 35.  The procedure implemented above does not follow the CoS procedure in the following case: If there is a tie for weakest candidate, the CoS procedure chooses the candidate who had fewer votes in the previous round, if one exists; otherwise, a candidate is chosen at random. ​ The procedure implemented here always chooses a candidate at random from among those tied for last place, regardless of the status during the previous round. ​ (This procedure is consistent with the University of Chicago [[http://​sof.uchicago.edu/​hare/​rules.html|rules]].) The procedure used by the College of Science is described in this [[http://​www.science.purdue.edu/​faculty_staff/​policies/​PP2006_11_16.pdf|document]],​ starting at page 35.  The procedure implemented above does not follow the CoS procedure in the following case: If there is a tie for weakest candidate, the CoS procedure chooses the candidate who had fewer votes in the previous round, if one exists; otherwise, a candidate is chosen at random. ​ The procedure implemented here always chooses a candidate at random from among those tied for last place, regardless of the status during the previous round. ​ (This procedure is consistent with the University of Chicago [[http://​sof.uchicago.edu/​hare/​rules.html|rules]].)
  
-===== How to Cast a Hare Ballot =====+====== How to Cast a Hare Ballot ​======
  
 Voters are given a list of candidates (a ballot), which they rank in order of preference: //c1//, //c2//, //c3//, ..., etc.  While it may appear that voters are selecting multiple individuals to fill the positions on the committee, they are not: Each voter'​s ballot will ultimately be cast for only //one// candidate. ​ The Hare Procedure moves ballots among candidates following rules that are intended to reflect the preferences of the voters. ​ The process stops when all (or nearly all) ballots have been assigned to the most popular candidates, who then make up the committee. ​   Voters are given a list of candidates (a ballot), which they rank in order of preference: //c1//, //c2//, //c3//, ..., etc.  While it may appear that voters are selecting multiple individuals to fill the positions on the committee, they are not: Each voter'​s ballot will ultimately be cast for only //one// candidate. ​ The Hare Procedure moves ballots among candidates following rules that are intended to reflect the preferences of the voters. ​ The process stops when all (or nearly all) ballots have been assigned to the most popular candidates, who then make up the committee. ​  
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   * Repeat for all //ci//.   * Repeat for all //ci//.
  
-===== Hare Process =====+====== Hare Process ​======
  
-==== Initial Step ====+===== Initial Step =====
  
 The first step in the process is to divide the ballots into sets based on the first candidate listed on each ballot. The first step in the process is to divide the ballots into sets based on the first candidate listed on each ballot.
  
-==== Selection Step ==== 
  
-In order to be selected, a candidate must have a minimum number of votes, called the //quota//, which is roughly the number of votes cast divided by the number of positions to be filled. ​ More precisely, the College of Science defines the //quota// to be //(votes cast + 1)/(number of positions + 1)// rounded up.+===== Selection Step ==== 
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 +In order to be selected, a candidate must have a minimum number of votes, called the //quota//, which is roughly the number of votes cast divided by the number of positions to be filled. ​ More precisely, the College of Science defines the //quota// to be //(votes cast + 1)/(number of positions + 1)// rounded up.  (As a side note, this quota calculation is actually closer to the "​Droop"​ quota than the "​Hare"​ quota, but we retain the older terminology to apply to the entire Single-Transferable-Vote process.)
  
   while there is a candidate that has the minimum number of votes   while there is a candidate that has the minimum number of votes
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 At this point, no remaining candidate has enough votes to be selected, so low-ranking candidates are eliminated and their ballots reassigned. At this point, no remaining candidate has enough votes to be selected, so low-ranking candidates are eliminated and their ballots reassigned.
  
-==== Elimination Step ====+===== Elimination Step =====
  
   choose a candidate randomly from those with the least number of votes   choose a candidate randomly from those with the least number of votes
hare_voting_procedure.1192455208.txt.gz · Last modified: 2007/10/15 06:33 by jtkorb