'Thankfully, most of us know more about voting systems than we realize: we're used to them from the X Factor, Eurovision, and lots of other contests that grip the nation every year.'

Dr Alan Renwick from the School of Politics and International Relation is an expert on electoral systems and electoral reform in the UK and around the world. With the impending alternative vote referendum on Thursday 5 May, Dr Renwick has provided his expert knowledge and opinions on the Alternative Vote to national media, including The Times, BBC News channel, BBC News website, and Radio 5.

Here is Dr Renwick's piece from The Times (Saturday 23 April 2011) - 'Bucks Fizz can help you make your mind up about AV'.

Unless you're a total elections junkie like me, you're probably either bored or bamboozled (or both) by the debate over AV. Most people get the fact that under AV you can rank the candidates. But then how are these preferences counted? Does AV give some voters extra votes? Is the weight AV gives to lower preferences fair?

Thankfully, most of us know more about voting systems than we realize: we're used to them from the X Factor, Eurovision, and lots of other contests that grip the nation every year.

To see the basic case for AV, look at the difference between Britain's Got Talent and the X Factor. BGT uses First Past the Post - the current Westminster system. There are ten contestants in the final; whoever gets most votes wins. The trouble is that if votes are widely spread across the contestants, victory could be secured on little more than a tenth of the vote. Someone with a small but committed following could win, even if the rest of the country despises them.

X Factor avoids this: after each round, the singer coming last is kicked out. Eventually only two remain and the winner has majority support. AV achieves basically the same without requiring us all to traipse back to the polls each week. With your first preference you say whom you want to win. Your second preference says whom you want to win if your top pick gets the boot - and so on. You can't change your mind under AV, as you can in the X Factor - but otherwise the logic is the same.

X Factor shows why the claim that AV gives some voters extra votes is wrong. You can vote once each week in the X Factor. That's true whether you vote every week for Matt Cardle or switch from loser to loser to loser. In AV too, if your first preference stays in the race, your vote for him or her is counted once in each round, just as it is if your vote is transferred from your first to your second to your third preference.

But how much do lower preferences weigh under AV? To get a handle on this, cast your mind forward to the glitterfest of Eurovision coming a week after the referendum. In Eurovision, each country ranks its top ten acts. The first gets twelve points, the second ten, and so on. The winner is the act with most points. That means that preferences are weighted: lower preferences give fewer points than higher preferences. But these preferences always count - which means you could scupper your favourite act's chances by giving ten points to your second favourite.

In AV, by contrast, lower preferences have the same weight as higher preferences - but only if they are counted. Your second preference is counted only if your first choice has been excluded. It's like first counting only the twelves. Only if no candidate has a majority of the twelves do you eliminate the act with fewest twelves and count instead the second preferences of their supporters.

Look at Britain's great triumph of thirty years ago, when Europe made its mind up for Bucks Fizz. Defenders of great British traditions should be aware that we would have lost under First Past the Post: Bucks Fizz gained only two twelves, tying for fourth place behind Switzerland, France, and Germany. They won because they secured lots of eights and tens - and because Eurovision counts these lower preferences.

The interesting thing is that we would have lost under AV too: with so few first preferences, we would have been eliminated before our deep well of middling support could have been tapped. So AV does give special weight to first preferences: you need a decent number of them to stay in the game in the early rounds of counting.

But this also points to a problem with AV: it counts some lower preferences but not others. This can lead to all sorts of weirdnesses: candidates can be harmed by winning more votes and helped by losing them. There are serious political scientists who say we should avoid this by electing our politicians not along X Factor lines, but on the principles of figure skating: voters would give each candidate a score; the candidate with the highest average score would win.

But that's another story: figure skating elections aren't an option in the referendum. The choice is X Factor v. BGT. The AV debate is less obscure than you thought.

Dr Renwick has also written ‘The AV Referendum: What's it all about?' in which he describes how the Alternative Vote works and what the Yes and No campaigns believe and his book ‘A Citizen's Guide to Electoral Reform' which describes the pros and cons of the various electoral systems.