The UK election—theoretical problems with single member district plurality systems

On May 6, the UK will be holding a general election, which will determine the composition of the House of Commons in Parliament going forward.  This election is particularly interesting, since it highlights one of the major quirks of the single member district plurality election system that is used in the UK.  It should be noted that this is similar to the voting for the House of Representatives in the U.S.

Of course, one of the major differences is that the UK Prime Minister is a member of the House of Commons himself who is only directly elected in his own district and is typically the leader of the party that wins a majority of the seats, whereas the President of the United States is elected by the entire nation.

So, with that in mind, the following chart shows the percentage of the votes and seats won by the three largest parties in Parliament over the course of the last 50 years, with the Labor Party in red, the Conservative Party in blue, and the Liberal Party, which merged with the SDP in 1981 and became the Liberal Democrats in 1988, in yellow.  The pastel colors represent the vote percentage while the bolder colors represent the seat percentage:

One can see that the plurality-winning party tends to win a majority of the seats and that the gap in seats between the governing and the opposition parties tends to be exaggerated when compared to the original vote gap.  It’s also quite clear that the third party has consistently won considerably fewer seats than would be expected if apportionment were proportional to the vote count.

This is classic trademark of a single member district plurality voting system—that is, where each seat is determined by which representative earns the most votes in each district.  Essentially, all votes that don’t go toward the plurality winner are wasted—they have no impact on the power structure in Parliament.  What this means is that the breadth of a party’s support only matters insofar as it can win plurality votes in individual, localized districts.

In the Liberal Democrats’ case, the party clearly has a broad base of support, winning 22% of the votes in the last election, but it only won 10% of the seats. Obviously, when compared to the Labour Party, which won 35% of the votes and 55% of the seats, and the Conservative Party, which won 32% the votes and 31% of the seats, the Liberal Democrats are significantly underrepresented in Parliament, whereas Labour is significantly overrepresented.

Of course, one could argue that maximizing the democratic element of an election is not a priority and perhaps even that an arbitrary filter between the will of the populace and the ideological representation of Parliament is a feature, not a bug.  Indeed, if the House of Commons had proportional representation, none of the parties would have won a majority of the seats in the past 50 years (indeed one would have to go back to 1935 to find such an election), and perhaps a single party government governs more effectively than a coalition.

However, in this election, such arguments look significantly weaker.  In a recent YouGov poll, the Liberal Democrats had a lead with 33% of those polled followed by 32% for the Conservative Party and 26% for Labour.  Despite this, even if such numbers held in the May 6 election, Liberal Democrats would still be the third party in Parliament, despite being the most popular in the election.  If what is termed as the “Liberal Democrat surge” continues, the result will likely be a hung Parliament and a coalition government, probably with Labour, the current ruling party.

While party lines are very important in British politics, the voting system is arranged as if geographical lines were the most important, which will be shown to be a mistake if the most popular party is also the most evenly spread.  Most other countries with Parliamentary systems manage to work in a proportional component to their elections, if not electing the entire Parliament by proportional representation.  If the Liberal Democrats can force a hung Parliament, it will be interesting to see what sort of electoral reform pledges they can draw out of a coalition partner.


About Meng Bomin

Real name Benjamin Main, I am a graduate of Grinnell College with a degree in Biological Chemistry.
This entry was posted in Current events, Musings, Politics. Bookmark the permalink.

1 Response to The UK election—theoretical problems with single member district plurality systems

  1. Just started my own blog on Blogspot need help with header?

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