This is the first in a series of posts I’ll be writing on electoral reform, based on a submission I sent into the Joint Oireachtas Committee on the Constitution recently. You can find the full series by clicking here.
When Proportional Representation by Single Transferrable Vote (PR-STV) was first established as Ireland’s electoral system in 1921, it was presented as an alternative to the first-past-the-post (FPTP) system employed in the UK. The main reason that the new system was adopted was that, as its name suggests, it is more proportional than FPTP, in that the number of seats each party wins should be roughly proportional to the share of the vote they receive. While PR-STV has certainly improved from FPTP in that regard (not a difficult feat, as FPTP is particularly disproportional), it is worth noting that Ireland was the first country to implement PR-STV in national elections, and hence there was little evidence at the time it was chosen with which to analyze its proportionality. With almost a century of elections now held under the system, however, there’s now a considerable amount of data with which to examine whether PR-STV fulfils its purpose of proportionality.
The above graph shows the correlation between the proportion of national first-preference votes (FPV) a party receives and the number of seats it wins as a result. It is based on the results of every party in every general election held since 1981 (the first 166-member Dáil), and each point on the graph represents a party’s result in one of those elections. The dashed red line represents a perfectly proportional allocation of seats according to national vote.
What’s immediately visible about our current PR-STV system from the graph is how it benefits the larger parties compared to a perfectly proportional system. In only one outlying case did either of the state’s two large parties win less seats than would have been allocated proportionally (FG, 2002), and in every other election they received a bonus from the PR-STV system. For Fianna Fail in the 1997 and 2002 elections, this bonus gave them an extra 12 and 13 TDs, respectively, over their representation in a purely proportional system.
The PR-STV system, as currently implemented, likewise disadvantages smaller parties. The second graph is enlarged to only show the results of parties that received less than 8% of the national FPV. It can be seen that in the considerable majority of cases, parties in this bracket win less seats than a proportional system would allocate them. Furthermore, there are often large variations in the number of seats won on a similar proportion of the vote. For example, between the 1992 and 1997 elections, the Progressive Democrats went from 10 to 4 seats, despite receiving exactly the same proportion of the national vote on both occasions (4.7%). In a perfectly proportional system, they would have won 8 seats in each election.