Voter Power Index

Today, Tuesday April 5th, sees the launch of a new version of the Voter Power Index (VPI) which I first created in 2005 to try to assess how much power voters really had in the UK.  As people familiar with my work with nef will know I am keen on creating relatively simple ways into complex issues as a way of opening space for debate.  Examples include the Happy Planet Index and Five Ways to Well-being, and the VPI is in this tradition.  The current First Past the Post (FPtP) system creates pointless inequalities in the distribution of the power of votes across the UK and I wanted to be able to create a single number that ‘held’ this issue.  By having geographically-based constituencies electing single members of parliament (MPs) the FPtP system creates ‘lumps’ of electoral power and thereby introduces potential inefficiencies in the way the will of the people is translated into the number of MPs elected from each party. As is well known some constituencies are so ‘safe’ that they are not really contested by any parties, with all focus on the ‘marginal’ seats that might actually change hands.  The VPI equates ‘power’ with the ability of electors to influence the results of their local constituency election and is a statistical representation of the contestability of a constituency.

In exactly a month’s time, Thursday 5th May, the UK will hold a nationwide referendum to decide whether we should switch to the Alternative Vote (AV) system of electing MPs.  AV still uses a system of single member constituencies but voters get to express their political preference as a ranking of candidates (1, 2, 3 …) instead of having to just choose one. AV clearly does not eliminate the ‘lumps’ of electoral power but by increasing the probability that seats will change hands it does mitigate some of the inequalities of FPtP.  This increase in probability of seats changing hands can be thought of as increasing the number of ‘very marginal seats’ – by my estimates up from 81 to 125, an increase of 44 seats.  Very marginal seats are defined as having a greater than 1 in 3 chance of changing hands and are clearly the most strongly contested with both turnout and the spending by the political parties significantly higher.

You can see what the impact of switching to AV might have on the power of your vote by visiting the Voter Power website, created and designed by web designer Martin Petts.

Voters will have to decide for themselves whether this increase in voter power is sufficient for them to vote YES on May 5th. Clearly the VPI does not hold everything that might be important in determining whether we should switch systems, but as a simple way into the issues I think it does have potential to open up space for a more (statistically) informed debate.

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One Response to Voter Power Index

  1. Wow that was odd. I just wrote an really long comment but after I clicked submit my comment didn’t appear. Grrrr… well I’m not writing all that over again. Anyways, just wanted to say fantastic blog!

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