Comparisons: Summary (Multiple-Winner) 1

Contrasting and complementary properties and features of party-list CHPV in relation to other multiple-winner voting systems that are highlighted in the preceding sections of this chapter are summarised below:

Party-List CHPV versus the Single Transferable Vote (STV)

• In STV, votes are transferred between the candidates to determine the winners.
• In CHPV, those party candidates with the highest averages win.
• Unlike CHPV, STV is a quota system; where a specific quota (such as Hare, Hagenbach-Bischoff and Droop) is used.
• Voters express preferences for candidates in STV elections but vote only for parties in closed-list CHPV ones.
• Nevertheless, with the addition of a free list, voters can rank the candidates within their chosen party; using the ranked ballot CHPV voting system for example.
• The CHPV algorithm involves just one simple count but the STV one is complex and requires many rounds of counting.
• The CHPV algorithm is transparent and deterministic whereas the STV one is neither.
• Both systems are employed in concurrent elections across multiple few-winner constituencies.
• Both systems achieve a high degree of optimality within few-winner constituencies.
• Both systems achieve a high degree of proportionality across multiple constituencies.
• Both systems only elect one type of member; with each winner having the same status and set of responsibilities.

Largest Remainder Party-List Methods versus Highest Averages Party-List Methods

• A largest remainder party-list method employs a specified quota that must be met or exceeded one or more times by a party for it to win one or more seats.
• A highest averages party-list method divides each party tally by a sequence of divisors to generate an 'average' for each candidate and only those with the highest averages are elected.
• Largest remainder methods satisfy the quota rule and are consequently highly party-proportional systems.
• This rule requires that a proportional but fractional seat allocation be rounded up or down to the nearest integer.
• However, obeying the quota rule can sometimes result in non-monotonic and paradoxical election outcomes.
• Highest averages methods are monotonic and never produce paradoxical election outcomes.
• However, as they do not satisfy the quota rule, they are slightly less party-proportional than comparable largest remainder methods.
• Party-list CHPV is a highest averages method that consecutively halves the tally 'average' for successive candidates on a closed party list.

Party-List CHPV versus the Hare Quota Party-List Method

• The Hare Quota is V/W; where V is the number of valid votes cast and W is the number of seats/winners.
• Both systems are party-list ones but the Hare Quota method employs the largest remainder approach whereas CHPV uses the highest averages one.
• Unlike CHPV, the Hare Quota method is an optimally proportional voting (OPV) system irrespective of the number of competing parties or the number of seats/winners.
• The optimality of the Hare Quota method is therefore 100%; while for CHPV it is always somewhat lower.
• Any disproportionality associated with the Hare Quota method is solely due to seat resolution whereas with CHPV the voting system itself also introduces some further disproportionality.
• However, the Hare Quota method is readily susceptible to parties seeking to gain an unfair advantage through cloning.
• In contrast, party cloning in few-winner CHPV elections is most likely to be counterproductive.
• The Hare Quota method is generally used in a multiple-winner constituency whereas CHPV is instead used in numerous few-winner ones.

Party-List CHPV versus the Droop Quota Party-List Method

• The Droop Quota is [V/(W+1)]+1; where V is the number of valid votes cast and W is the number of seats/winners.
• Both systems are party-list ones but the Droop Quota method employs the largest remainder approach whereas CHPV uses the highest averages one.
• In two- or three-party contests, the optimality of both the Droop Quota and CHPV is over 70% for up to five winners.
• Only for three or four winners in such contests, does CHPV have a higher optimality than the Droop Quota method.
• The Droop Quota method is not as susceptible to party cloning as is CHPV.
• However, for up to five winners, cloning attempts by the minority party in CHPV will fail.
• In a two- or three-party election, it is only for three or four winners that CHPV produces results that are more party proportional than the Droop Quota method.
• For elections with few winners and few parties, the Droop Quota and CHPV systems generate comparable party-proportional outcomes.
• The Droop Quota method is generally used in a multiple-winner constituency but CHPV is instead used in numerous few-winner ones.

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