It will come as little surprise to long-time readers of this blog that I will be voting yes in the alternative vote referendum on Thursday. But now that the focus of this blog is less on politics, I haven’t actually written much about it. With just a few days to go, until polling day, I have decided that now is the time.

The deceptive claims of the No to AV campaign have been comprehensively taken apart umpteen times elsewhere, I am sure. But one section of the No to AV leaflet particularly irritated me.

It shows a group of four runners crossing a finish line on a running track. A big arrow points to the trailing runner who appears to cross the finish line in fourth place: “The winner under AV”. The message? “Awooga! AV is unfair because the loser wins!”

I don’t know a great deal about athletics, but I am pretty sure that there is a fixed finish line. The first person to complete the set distance wins the race. It might be 100 metres. In this photograph here, it is the man in blue who ran 100 metres first.

But what is the distance in a voting system? I have tried to work out what it is under first past the post, but I cannot tell. Here are some examples from last year’s UK General Election. Can you see where the finish line is?

It is pretty clear in Kirkcaldy and Cowdenbeath, where I used to live. With 64.5% of the vote, a clear majority were in favour of the Labour candidate.

In my neighbouring constituency of Dundee East it is somewhat less clear. No party received a majority of the votes. Second-placed Labour took 33.3% of the vote. But the winning SNP took 37.8%. It’s not very cool. The SNP might not be what the majority of voters wanted.

Anyway, we have narrowed the first past the post winning threshold down to something between 33.3% and 37.8%.

But looking at the results for Argyll and Bute, the “finish line” analogy becomes really confusing. The first-placed Lib Dems took only 31.6% of the votes. But Labour had 33.3% of the votes in Dundee East, and came only second there.

In first past the post, the finish line changes position. In fact, there is no finish line. It doesn’t matter if you don’t get a majority of the votes. Theoretically you could get an extremely low share of the vote, far from a majority, yet still win under first past the post.

So which is the system where the loser can win?

Alternative vote sets a threshold where candidates must aim to gain the support of the majority of voters. A candidate is not deemed to be the winner until he crosses the finish line, which is unambiguously 50%.

(It is theoretically possible for a candidate to win under alternative vote without crossing that threshold — but only in unusual circumstances and after all other options have been exhausted.)

Alternative vote may not be perfect (although the perfect voting system doesn’t exist anyway). But it is a whole lot more desirable than the current rotten system.