STV: the benefit nobody talks about

British democracy was created in the 19th century, like the railways. Like the railways it was, for its time, truly world-leading. However after 150 years, like the railways, it is showing its age. People, technology and society have come a long way, and a system which worked yesterday needs to be adapted and improved for the different conditions of today.

One flaw which is becoming increasingly apparent is the way it stifles minorities. Under the first-past-the-post system the winner takes all and the loser gets nothing. Democracy has to be more than that. Even in a simple two party system, 49% of the voters may have no say in how the country is run – and in a multiparty system the ruling party may have the support of well below half of the population.  In a balanced system where the pendulum of power swings to and fro this may not matter too much, but when the difference is structural a large minority is rendered permanently powerless, which in the long run invites revolution.

These arguments are well rehearsed and various schemes to improve proportionality are suggested: the party list system, as was used in the Euro elections, the additional member system, as is used in the regional assemblies, the alternative vote and the Single Transferable Vote. Pundits with spreadsheets discuss the improvements in ‘proportionality’ given by the various schemes. I want to make a point in favour of the STV scheme which has nothing to do, directly, with proportionality. It gives voters the chance to choose their MP from within party list.

Let’s take a town of 200,000 people. Under STV its voters elect three MPs.  Suppose, for simplicity, there are only two parties: Left and Right.   The town is fairly evenly balanced, and elects 2 Left and 1 Right MP in some elections and 2 Right and 1 Left in others, depending on the way the political wind is blowing. 

Now, although each party knows that the best it can hope for is 2 seats out of 3, they will put up 3 candidates. Not to fill the slate will be seen as a sign of weakness.  This happens. To take an example close to home, in the last Euro elections (2019) here in the North West region all the parties (Conservatives, Labour,  Liberal Democrats, Brexit, Change, UKIP and the Greens) all put up full slates of 8 candidates, although they knew that they were never going to win all of them. The picture was the same in other regions. Parties will put up as many candidates as there are seats to be won.

So when a voter in this hypothetical town goes into the polling booth their ballot paper has six names, and they rank them in order (and although the mechanics of counting STV votes are complicated, its use by voters is really simple).  A staunchly pro-Left voter will write 1, 2 and 3 against the Left candidates and 4,  5 and 6 against the Right candidates: a pro-Right voter will do the reverse.  In doing so they are not only expressing their allegiance to a party, they are also expressing their preference for the candidates within that party.   And that preference carries through to the result.

Let’s see how that works.  Suppose that Smith, Jones and Robinson are the candidates for the Left party, which is doing well this time, while Brown, Green and White are standing for the Right party, which is lagging. Smith (a prominent local character) is more popular than Jones (a relative newcomer of whom little is known), while Robinson (whose controversial twitter stream has annoyed many people) is least popular of the three.   As the votes are counted the popular Smith is the first to reach the quota (more than one quarter of the votes cast).  Smith is elected, and surplus votes are diverted to the Jones pile.  

Even with that boost, perhaps neither Jones nor anyone else makes quota.   For the lagging Right party, Brown is the most popular candidate, followed by Green and then White, so the unfortunate White has the smallest number of 1st preference votes and is eliminated, their votes going to Brown who now makes quota.  Robinson is eliminated next,  their votes going to Jones who narrowly beats Green.   Yes, proportionality has worked, after a fashion, in that the town has elected two Left and one Right MP,  but it has done more than that: it has chosen between the candidates within the parties.

Everybody’s vote counts. There may be cases where a ballot is not counted for the voters preferred party – because the candidate made quota or dropped off the bottom – but their 4-5-6 ranking is used to express a preference as to which candidate of their non-preferred party gets elected. And so far we’ve ignored cross-party voting, which will strengthen the effect: voters are not tied to party allegiance and may vote for a popular individual despite their party.

STV also gives a much-needed voice to the majority. There is much – valid – complaint that in a ‘safe’ seat, voters for the losing parties have no say. But voters for the winning party have no say either.  The candidate is appointed by a small selection committee, or by party headquarters.  With STV it may still be effectively built-in that a party is bound to get a seat, but which of the candidates benefits from this is in the hands of the voters. Candidates – and sitting MPs – are going to realise this. They will be aware that they are answerable to the electorate rather than the party machinery. Today a Tory MP in the shires or a Labour MP in the industrial north knows that it would take major misbehaviour on their part to make voters switch party and thereby lose their seat, but with STV they will need to fear a switch in preference within the party ticket, and will treat their voters with much more respect.

This will change the dynamic of elections. Candidates will have to appeal to the electorate not just for their party but for themselves. Bright young SPADs who work the system within the party organisation to get onto the candidate list will also have to appeal to the electors if they’re going to get elected.  It’s worth noting that this dynamic is the opposite to the ‘party list’ system. You sometimes hear people object to PR because it gives control to the party rather than the voter; this applies to the list system but for STV it’s just the opposite.

Hopefully, in 100 years time “safe seats” will have gone the way of rotten boroughs and be consigned to history. STV can make that happen, giving choice to the people rather than the party machinery. 

The Lesson from the Prisoner’s Dilemma

This is a classic puzzle which, like all such, comes in the form of a story. Here is one version:


Alice and Bob are criminals. No question. They have been caught red-handed in a botched robbery of the Smalltown Store, and are now in jail awaiting trial.

The police have realised that Alice and Bob match the description of the pair who successfully robbed the Bigtown Bank last month. They really want to get a conviction for that, but with no evidence apart from the resemblance they need to get a confession.

So they say to Alice: “Look, you are going to get a 1 year sentence for the Smalltown Store job, no question. But if you co-operate with us by confessing that the two of you did the Bigtown Bank heist then we’ll let you go completely free. You can claim Bob was the ringleader and he’ll get a 10 year sentence.”

Alice thinks a moment and asks two questions.

“Are you making the same offer to Bob? What happens if we both confess?”

The police tell her that yes, they are making the same offer to both of them. And if both confess, they’ll get 6 years each.




OK, that’s the story. All that circumstantial detail is just to lead up to this decision table, which Alice is now looking at:

Bob
Confess Deny
Alice Confess 6+6 0+10
Deny 10+0 1+1

That’s the problem in a nutshell. Before we look at it there are maybe a few points to clear up

  • Alice and Bob are not an item. They are just business partners. Each is aiming to minimise their own jail term, and what happens to the other is irrelevant for them.
  • ‘Go free’ really does mean that – there are no vengeful families or gang members to bring retribution on an informer.
  • Whether they actually committed the Bigtown Bank job is completely irrelevant to the puzzle.

OK, let’s get back to Alice. She reasons as follows:

“I don’t know what Bob is going to do. Suppose he denies the bank job. Then I should confess, to reduce my sentence from 1 year to zero. But what if he confesses? In that case, I’d better confess too, to get 6 years rather than 10. Whichever choice Bob makes, the better option for me is to confess. So I’ll confess.”

Bob will, of course, reason the same way. If Alice denies, he should confess. If Alice confesses, he should confess. 0 is less than 1, and 6 is less than 10. Therefore he should confess.

The logic is irrefutable. But look at that table again. The prisoners have firmly chosen the top left box, and will both serve 6 years. That’s a terrible result! It’s not only the worst total sentence (12 years), its the next-to-worst individual sentence (6 years is better than 10, but much worse than 0 or 1). Clearly the bottom right is the box to go for. It’s the optimal joint result and the next-to-optimal individual result.

That is obvious to us because we look at the table as a whole. But Bob (or Alice) can only consider their slices through it and either slice leads to the Confess choice. To see it holistically one has to change the question from the Prisoner’s Dilemma to the Prisoners’ Dilemma. That’s only the movement of an apostrophe, but it’s a total readjustment of the viewpoint. A joint Bob+Alice entity, if the police put them in one room together for a couple of minutes (but they won’t), can take the obvious bottom-right 1+1 choice. Separate individual Bob or Alice units, no matter how rational, cannot do that.

This is what the philosophers call emergence. The whole is more than just the sum of its parts. A forest is more than a number of trees. An animal is more than a bunch of cells. It’s generally discussed in terms of complex large-N systems: what’s nice about the Prisoner’s Dilemma is that emergence appears with just N=2. There is a Bob+Alice entity which is more than Bob and Alice seperately, and makes different (and better) decisions.

There’s also a lesson for politics. It’s an illustration of the way that Mrs Thatcher was wrong: there is such a thing as society, and it is more than just all its individual members. Once you start looking for them, the world is full of examples where groups can do things that individuals can’t – not just from the “united we stand” bundle-of-sticks argument but because they give a different viewpoint.

  • I should stockpile lavatory paper in case there’s a shortage caused by people stockpiling lavatory paper.
  • When recruiting skilled workers it’s quicker and cheaper for me to poach yours rather than train my own.
  • My best fishing strategy is to catch all the fish in the pond, even though that leaves none for you, and none for me tomorrow.
  • If I get another cow that will always give me more milk, even though the common grazing we share is finite.

Following the last instance, economists call this “The tragedy of the commons”. It’s the point at which Adam Smith’s “invisible hand” fails.

This tells us something about democracy. A society or a nation is more than just the individuals that make it up. E pluribus unum means that something larger, more powerful and – dare one say it – better can emerge. So democracy is more than just arithmetical counting noses, democracy provides the means whereby men and women can speak with one voice as a distinct people. That’s the ideal, anyway, and – even if the form we’ve got is clunky and imperfect – some of us still try to believe in it.