If, like me, you live in a safe seat, then you’re probably not looking forward to May 6. There’s little more depressing than trudging down to the polling station to ‘do your democratic duty’ knowing full well that the only power your vote has is symbolic. It’s little wonder that increasing numbers of us are staying at home.

For people living in the 60% of seats which have almost no chance of changing hands this year, there’s a real sense that our electoral system is failing in its first duty: as the mechanism which connects us, citizens of this country, to our representatives in Westminster. But as a statistician my first instinct is not just to get mad, but to get measuring. That’s why I’ve designed the Voter Power Index which aims to measure, constituency by constituency, just how well or badly our system is using our votes.

To develop the index, I examined the two main factors which determine the impact of a vote cast in a given constituency:  the number of registered voters and the chance that the seat might actually change in hands. Clearly, the larger the number of voters in a constituency, the less power each individual has. Equally, the greater the probability that a seat might change hands, the more valuable each individual vote. To estimate the chance of the seat changing hands, I produced a probabilistic model based on data from general elections from 1954 to 2005. The model predicts the chance of a change of party, based on the majority of the sitting MP.

When I first calculated the index, even I was staggered just how little most people’s votes count.  It quickly became clear that our current system is hugely inefficient at translating the will of the people into the result of a general election.  In fact, the VPI allows us to put a number on the level of this inefficiency – 75% of voting power is wasted. The vast bulk of the power which should be exercised by British voters is lost in votes for non-winning candidates which are simply discarded  (this represented more than half of all voters in 2005) and in large, meaningless majorities.

By contrast, a fully proportionate system might approach 100% efficiency. For example, the2004 European Elections were about 96% efficient.

Not only is the system inefficient it is also chronically unjust. Voter Power is hugely unevenly distributed in the UK, with the most powerful 20% of voters having over 33 times more power than the least 20%.  Note that this is a far more uneven distribution than household income in the UK. Even before the redistribution through taxes and benefits – the richest 20 per cent of households ‘only’ earn 15 times as much as the poorest. After redistribution this inequity factor is reduced to under 4 times.

This year, as we approach another election, it’s more important than ever that ever that the scandal of our inneffectual, unfair electoral system is exposed. That’s why it’s great that web-developer Martin Petts has created a Voter Power Index website that lets everyone simply find out how much their vote is really worth. 

The Voter Power Index shows that our current system is profoundly undemocratic. It gives vastly more power to some voters than others. It betrays the fundamental principle of democracy:  one person one vote.  It is high time we changed the whole rotten system.

Nic Marks is a fellow at nef (the new economics foundation)

Find your voter power at www.voterpower.org.uk

The Voter Power Index was first published as the Index of Democratic Power in a 2005 report called Spoiled Ballot and published by nef (the new economics foundation).