Friday, 9 June 2017

Why did Corbyn do so well? A little bit of political economy

Let's assume the exit poll is about true, and that Jeremy Corbyn has done even better than the polls thought – and he was already pulling far ahead of what people, including me, expected.

There are lots of things to say about this: failures in polling (again); Theresa May's incompetent campaign and feeble personality; Jeremy Corbyn's quality as a campaigner; the role of the internet.

I think one dog that very importantly did not bark is the Labour manifesto. Remember, Jeremy Corbyn is a passionately ideological Leftwinger. But the manifesto was in many ways rather moderate. It did not, for example, aim to spend much more than the Conservatives. It did not set out to reverse many Conservative welfare cuts.

A classic model in political science explains why parties move to the centre. Suppose the two parties are concerned only to win the elections. They will each promise a platform right in the middle of the electorate, at the famous "median voter" - the person in the middle, who has half the electorate to the left of her and half the electorate to the right. Why? Because if one candidate moves to the left of this person, then (at least!) everyone on the right votes for the other candidate, who wins a 50% majority. And if one candidate moves to the right, then everyone on the left votes for the other candidate who again wins.

Here's an ASCII art picture. It shows a line representing political preferences from Left to Right. The voters are at x. The median voter is marked with a *, with two voters on her left and two on her right. Voters vote for the party that is closest to them. Both parties will propose a platform at *. Any party that moved left or right would get three voters preferring the other candidate.


A natural response to this is "oh, but politicians are idealists! Or at least, Jeremy is. Jeremy cares about policy, not just getting elected." Well, stop swooning over Jeremy for a second, and suppose that is true. Suppose you are Jeremy Corbyn and deeply want policy to be as left wing as possible. You will still move to the centre. For, if you do not, and lose, then you will get the policies implemented by your right wing opponent.

This seems to be what has happened. Corbyn moderated his manifesto. That made Labour palatable to voters who would never have tolerated Corbyn's own ideal policies.

In a sense, you could say that despite appearances, the ghost of Blair still haunts the Labour party. Even with Corbyn as leader, they are forced to go along with a lot of the consensus of the past forty years.

(Thank God! ... But this is a post about the "horse race", not the outcome.)

The original model of the median voter is the "Downsian" model, made famous by Anthony Downs' An Economic Theory of Democracy (1957); but actually first suggested by Hotelling (1929) "Stability in competition". The point about "idealistic" politicians was first made, I think, by Donald Wittman (1929) "Candidates with policy preferences: A dynamic model" – sorry no ungated version.