A brief examination of New Zealand’s approach is illustrative here:
- 70 constituencies (“electorates”) — of which 7 are Mâori constituencies, to represent people of Mâori ethnicity or ancestry. (Elected by FPTP)
- 50 party-vote seats. (Elected from party-lists)
- Nominally, the number of seats in the legislature is the total of the number of constituency seats, plus the number of party-vote seats, which is 120 seats.
- Actual seat-counts can be slightly higher or lower — due to the number of party members elected to constituencies being higher than their party-vote eligibility (“overhang”), or not having enough members in the party-list to enable full allocation of seats by party-vote eligibility (“underhang”).
For a general election:
- Parties submit (closed) lists of individuals endorsed by the respective party, in order of preference as determined by the respective party.
- Any members elected to a constituency seat are removed from the party-lists.
The number of party-vote seats for which a party is eligible is determined, the number already elected to constituencies is deducted from this, and the remaining number of seats are then allocated from the party-list:
“In order to participate in the proportional allocation of House seats, a party must receive at least five percent of all valid party votes cast, or win at least one electorate seat…
“The electorate seats won by a party at the constituency level are then subtracted from the total number of seats allocated to that party’s list, and the remaining seats are filled by the candidates on the party list in the order determined before the election.
“In some instances, a party may win more electorate seats than the number of seats it is entitled to according to the result of the party vote. In such cases, the party keeps the overhang or surplus seats, and the total number of seats in the House is increased accordingly. This was the case in the 2005 general election, in which the Mâori Party won four electorate seats, but was awarded a total of three seats. The party retained its overhang seat, and the House of Representatives was expanded from 120 to 121 members.” — Elections to the New Zealand House of Representatives
- If the party list is exhausted before the number of seats to which the party is eligible are allocated, the party’s remaining party-vote seats are left vacant. (Underhang)
- Once seats are allocated in the general election, whether by constituency vote or assignment from party-lists, they are not reallocated as members’ affiliations or party allegiances might change.
- In the event of a constituency vacancy, a by-election for that constituency is held (no party-vote for by-elections), the outcome of which does not affect the already-established party-list-assigned seats.
- In the event that a party-list-assigned seat is vacated, the next person on the party-list submitted by that party for the prior general election, is selected — providing that such person is still a member of the party, and willing to serve. If there is no such person remaining on the list, the seat remains vacant.
This answers some of my own concerns about party-based proportionality: while being on good terms with the party is, of course, necessary in order to get the party nomination in the first place, a disagreement in office, though it might affect the member’s prospects for the next general election, and fair-enough if so, it does not put the member’s current seat-holding at risk; this affords a measure of scope for dissent and debate in office.