Proportional representation: Difference between revisions
→Proportional Representation Criteria
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Since the standard definitions of Proportional Representation do not apply to nearly all modern systems it has become common to define proportional representation in terms of passing some sort of criteria. There is no consensus on which criteria need to be passed for a parliament to be said to be proportional.
=== [[Proportionality for Solid Coalitions]] Criterion ===
If a sufficiently-sized group (generally at least a Droop or Hare quota) prefer a set of candidates above all others, do at least a proportional number (being the number of quotas the group comprises rounded down to the nearest integer) of candidates from that set (supposing there are enough of them) get elected?
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Semi-Proportional systems can be constructed from any multi-winner system. However, they are typically done with sequential non-partisan systems, such as the [[single transferable vote]] and [[Reweighted score voting]].
An alternative, perhaps more common definition of semi-proportional is that a voting method must pass some weak form of [[Proportionality for Solid Coalitions]] e.g. allowing voters to get PSC-like outcomes through strategic voting. Something like [[SNTV]] would classify as semi-proportional under this definition.
==Advocacy==
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==Non-Partisan Definitions==
In the case of non-partisan voting, the definition of proportional Representation is undefined. Metrics like Gallagher index can no longer be defined. For non-partisan multi-member systems, for ranked methods, there is generally one minimum requirement for proportionality, [[Proportionality for Solid Coalitions]] (though see the [[Monroe's method#Fully Proportional Representation with Ordinal Balloting|Monroe's method]] article for an alternative idea), while for cardinal PR methods, there are four main competing philosophies between what is and is not proportional: [[Phragmén's Method | Phragmén]], [[Monroe's method | Monroe]], Thiele and [[Vote unitarity | Unitary]].
* Proportionality for Solid Coalitions (PSC) requires that when quotas of voters prefer sets of candidates above all others, a proportional number of candidates from those sets must be elected.
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* Under the [[Monroe's method | Monroe interpretation]], voting is an attribution problem where every candidate has a [[Quota | quota]] of voters to be filled with specific voters. The winner set composed of candidates which maximizes the sum of score for the voters in that candidate’s quota is the most proportional. The voting method is impartial to how anybody outside of that candidate’s quota rates them.
* Under the Thiele interpretation, voters have vote weight which should be distributed across candidates. The proportion of ballot weight assigned to each winner is the amount which that candidate supports their election. Under this interpretation, the more an outcome maximizes the sum of all score when reweighted by ballot weight, the more proportional it is.
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! System !! Philosophy !! Comment
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| [[Single transferable vote]]|| [[PSC]] or
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| [[Sequential Monroe voting]]|| [[Monroe's method | Monroe interpretation]]|| -
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