Tutorial 7: Introduction to compensatory systems

In this tutorial we will learn how to define compensatory systems, used to level seats according to a second criterion.

Scotland - Scottish Parliament (Highlands and Islands)

A voter must cast two ballots:

  • First vote: an individual candidate will be chosen for a one-seat constituency, like in UK - General election (Caerfyrddin), winners will be elected by first-past-the-post.

  • Second vote: in order to improve the proportionality at a party level, a second part vote is performed for a region, comprised by several constituencies. The seats will be allocated using the highest averages method with d'Hondt divisors, resuming the already allocate seats.

We will use only the Highlands and Islands region: 8 constituencies and 7 additional members.

  1. Define the constituencies (first vote). Independent candidates can only win 1 seat.

     1name: Scottish Parliament - 2011
 2type: group
 3method: first_past_the_post
 4divisions:
 5
 6- name: Highlands and Islands
 7  type: group
 8  divisions:
 9  - name: mp_highlands_islands
10      type: group
11      divisions:
12      - name: Argyll & Bute
13        candidates:
14        - {alliance: SNP, name: Michael William Russell, votes: 13390}
15        - {alliance: Conservative, name: Jamie McGrigor, votes: 4847}
16        - {alliance: Labour, name: Mick Rice, votes: 4041}
17        - {alliance: Liberal Democrat, name: Alison Hay, votes: 3220}
18        # independent
19        - {max_seats: 1, name: George Doyle, votes: 542}
20        - {alliance: Liberal Party (The), name: George Alexander White, votes: 436}
21      - name: Caithness, Sutherland & Ross
22      - name: Inverness & Nairn
23      - name: Moray
24      - name: Na h-Eileanan an Iar
25      - name: Orkney Islands
26      - name: Shetland Islands
27      - name: Skye, Lochaber & Badenoch

  2. Add a compensatory district for the Highlands and Islands region:

     1name: Scottish Parliament - 2011
 2type: group
 3method: first_past_the_post
 4divisions:
 5
 6- name: Highlands and Islands
 7  type: group
 8  divisions:
 9  # regional additional member district
10  - name: am_highlands_islands
11    type: compensatory
12    mode: additional_member
13    seats: 7
14    method: highest_averages
15    method_params:
16      divisor_f: dhondt
17    first_vote: "alliance[mp_highlands_islands:-1]"
18    skip_initial_seats: yes
19    candidates:
20    - {name: SNP, votes: 85082}
21    - {name: Labour, votes: 25884}
22    - {name: Conservative, votes: 20843}
23    - {name: Liberal Democrat, votes: 21729}
24    - {name: Green, votes: 9076}
25    - {name: Scottish Christian Party, votes: 3541}
26    - {name: UK Independence Party, votes: 3372}
27    - {name: All Scotland Pensioners Party, votes: 2770}
28    - {name: Ban Bankers Bonuses, votes: 1764}
29    - {name: Liberal Party (The), votes: 1696}
30    - {name: Socialist Labour Party, votes: 1406}
31    - {name: British National Party, votes: 1134}
32    - {name: Scottish Socialist Party, votes: 509}
33    - {name: Solidarity, votes: 204}
34  # one-seat constituencies
35  - name: mp_highlands_islands
36    type: group
37    divisions:
38    - name: Argyll & Bute
39    - name: Caithness, Sutherland & Ross
40    - name: Inverness & Nairn
41    - name: Moray
42    - name: Na h-Eileanan an Iar
43    - name: Orkney Islands
44    - name: Shetland Islands
45    - name: Skye, Lochaber & Badenoch

    The addtional_member adapter will resume a previous allocation using a different method. Setting skip_initial_seats to true, only the new allocated seats will be included in the node result.

    The first vote is taken from leaf nodes from mp_highlands_islands, and transformed to taken the alliance as identifier.

New Zealand - General Elections

The system is really similar to the Scotland’s one, but there are some differences:

  • There is only one compensatory district for all the country.

  • The compensatory district will not resume the previous allocation. A big number of seats are assigned so that the disproportionality will be absorbed. The seats won by constituencies will be subtracted from the result.

  • For a party to participate in the compensatory allocation, it must reach a 5% of the formal votes. That won’t apply to parties that won at least 1 constituency.

 1name: New Zealand General Elections - 2014
 2method: first_past_the_post
 3type: group
 4divisions:
 5# mixed member district
 6- name: compensatory district
 7  type: compensatory
 8  mode: mixed member
 9  method: highest_averages
10  method_params:
11    divisor_f: sainte_lague
12  seats: 120
13  exclude: votes < 5%
14  include: electorate vote.alliance_seats >= 1 => alliance
15  first_vote: alliance[electorate vote:-1]
16  skip_initial_seats: yes
17  candidates:
18  ...
19# constituencies
20- name: electorate vote
21  type: group
22  aggregate: true
23  divisions:
24  ...

The mixed_member adapter allocates again using the second vote, and it subtract the seats won by the first allocation.

Well… as you can see, this is escalating. Take some rest and bring a fresh change of clothes, because we are travelling to Northern Europe, home to complex compensatory systems. Things could happen…