The worst electoral system, apart from all the others

This article first appeared in the Daily Telegraph online on 24 March 2015

Expect a push for PR after 7 May.

Expect that shortly after the election, people will start to talk about proportional representation (PR). Liberal Democrats, Greens and even UKIP supporters will all talk about the unfairness of Britain's first-past-the-post (FPTP) electoral system. Others will question why the SNP has so many seats and, potentially, so much influence at Westminster.

Let's do a thought experiment. Suppose we listened to the voices for change and switched our system. For comparison, let's use a simple full PR system where a party's seats are strictly proportional to the number of votes it receives. There are other fancier PR systems around, but since we are focusing on larger parties anyway (over 5% of the votes regionally), there won't be much difference.

The graphic shows how many seats each party would win under both PR and FPTP, using Electoral Calculus' current best predictions for vote share and predicted FPTP seats. Labour is still the largest party, with 213 seats, but the Conservatives are close behind on 201 seats. Now politicians have to put a coalition together which has at least 326 MPs. However there are no possible two-party coalitions, other than the unlikely Con/Lab combination.

Any coalition would have to be an unwieldy three-, four- or even six- party affair. Possibilities include: Lab+SDLP+Lib+Green+SNP+PlaidC (with only 328 seats), or Con+UKIP+Lib (with 349 seats but hard to manage), or Con+UKIP+Green (with 337 seats, but even trickier). It would be a recipe for fractious and fractured government.

Before we junk the current system due to a single election result, it's worth having a look at how it has actually performed over the longer term. In the 115 years since 1900 there have been twenty-nine elections. The average vote share for the three major parties over that time has been Con 44 pc, Lab 33 pc and Lib 19. Compare this with the amount of time that the three parties have spent in government (counting coalitions as half-government) to see what fraction of "governing time" has been awarded to each party. Those figures are: Con 54 pc, Lab 29 pc and Lib 12 pc.

Now those are not quite exact matches - the Conservatives have done a bit better than they deserve and the Liberals a bit worse. But it is not an appalling outcome that flies in the face of democracy. And PR is not without blemishes either. Some small parties can spend a long time in government as part of a coalition under PR, which would be out of proportion to their popular support.

There is even an actual mathematical proof, called the Arrow Impossibility theorem, which proves that there is no ideal electoral system in a multi-party framework. No system is perfect.

So when the losers clamour for change after the May election, we should resist their calls to chase the illusion of perfectability.

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