Modelling a larger Senedd under List PR
ERS Cymru briefing for the Special Purpose Committee on Senedd Reform 2
Further to our modelling of a larger Senedd under AMS, STV and a 5 region based List PR system, we have undertaken additional modelling on List PR. This models an 80-, 90- and 100-seat Senedd under a List PR system based on pairing the 40 existing constituencies into 20 constituencies.
Methodology
With the caveats that It is important to note that it is impossible to predict with complete certainty the outcome of a particular election if it had been held using a different voting system still standing, the projections that follow are an indication of what the results of the 2021 Senedd election – conducted under AMS – may have looked like if a List PR system had been used.
List PR projection
Given limitations of modelling a Flexible List system, for this projection we followed the variant of List PR formerly used in Great Britain for elections to the European Parliament (Northern Ireland used STV for these elections).
We paired each of the current 40 First Past The Post (FPTP) Senedd constituencies into 20 multi-member STV constituencies, each with between three to six members, depending on the size of the electorate of the new paired-constituency and the overall number of seats in the Senedd. We produced projections for a Senedd of 80, 90 and 100 members. We created the 20 paired-constituencies by pairing the current 40 FPTP constituencies for the same two reasons listed in the STV methodology above. We have no firm views on the optimum specific constituency boundaries for a List PR-elected Senedd based on 20 constituencies at this stage.
Regional list votes for each party at the 2021 Senedd election were added up across the paired-constituencies. Seats were allocated in each paired-constituency (between three and six) using the D’Hondt formula as for the regional list PR in our previous modelling.
Results
80 member Senedd based on 20 paired constituencies
|
Party |
Lab |
Con |
Plaid Cymru |
Total Seats |
|
Total seats under STV modelling |
37 |
25 |
18 |
80 |
|
Percentage of seats under STV modelling |
46.3% |
31.3% |
22.5% |
100.0% |
90 member Senedd based on 20 paired-constituencies
|
Party |
Lab |
Con |
Plaid Cymru |
LD |
Total Seats |
|
Total seats under STV modelling |
44 |
26 |
19 |
1 |
90 |
|
Percentage of seats under STV modelling |
48.9% |
28.9% |
21.1% |
1.1% |
100.0% |
100 member Senedd based on 20 paired-constituencies
|
Party |
Lab |
Con |
Plaid Cymru |
LD |
Total Seats |
|
Total seats under STV modelling |
50 |
29 |
20 |
1 |
100 |
|
Percentage of seats under STV modelling |
50.0% |
29.0% |
20.0% |
1.0% |
100.0% |
