Strictly Come Dancing / Leighton Vaughan Williams / 15 December 2008 / Leave a comment

Why did nobody get evicted from Strictly Come Dancing on Saturday night? The Betfair Prof explains...

Last year the betting public, along with most of the nation, were surprised by the outcome of the X Factor finals. This year balance was restored, as favourite Alexandra Burke sang her way to an expected victory.

Sunday's 'BBC Sports Personality of the Year' was less predictable, with an unusually hotly contested gong going to third favourite and Olympic cycling titan, Chris Hoy. The victory meant that he was essentially swapping pre-show expectations with favourite and pride of Mansfield, Rebecca Adlington. I was personally advised of this eventuality in the strongest possible terms a week earlier by my 11-year old nephew, but of course preferred to side with the wisdom of the crowd. That's my own fault, though my poor judgement was at least not the result of a misunderstanding of the rules of the competition. Which is more than can be said for many of those who plunged on two of the three dancing couples left in the 'Strictly Come Dancing' semi-finals after the voting lines opened!

For those unattracted to Saturday's dancing spectacular, let me briefly explain. The three couples left in the semi-finals of the competition perform two dances each, each dance marked out of 10 judged by four resident judges. The maximum score for each couple is, therefore, 80 points (four tens for each dance). In the event, one couple (Tom Chambers, of Holby City, and Camilla Dallerup) scored a total of 67 points for their Jive and Tango. The other couples scored a total of 75 points apiece, led home by the vivacious Quickstep of Lisa Snowdon (former 'squeeze' of George Clooney) and Brendan Cole, and the exquisitely performed Argentine Tango of Rachel 'S Club' Stevens and Vincent Simone.

Now comes the clever bit. According to the scoring system, those at the top of the judges' leaderboard are awarded points equal to the number of contestants (in this case, three). Those at the bottom are accorded a single point. The same system is applied to the public telephone vote. Now let's apply a little bit of elementary arithmetic to this and we can see that there are only the following possible results:

- Tom and Camilla: 1 point (from the judges) + 1, 2 or 3 points (from the public)
- Lisa and Brendan: 3 points (from the judges) + 1, 2 or 3 points (from the public)
- Rachel and Vincent: 3 points (from the judges) + 1, 2 or 3 points (from the public)

The best combined tally for Tom and Camilla is, therefore, 4 points (if they top the public vote).

The worst combined tally for the other couples is also 4 points but one must score at least 5 points.

Now add into the mix the fact that the bottom two couples (in the combined points tally) dance off in front of the judges, with one being eliminated, and what do we arrive at?

Exactly! Tom and Camilla are doomed for the dance-off before a single public vote is cast, and so all those precious votes cast for them are wasted. Having made the mistake of allowing the public to vote, the BBC had no choice when they spotted their error but to cancel the dance-off, usher all three couples into the final, and carry over the public vote. Not that this was spotted by those dominating the markets, as pre-show favourites Tom and Camilla drifted alarmingly before being restored to the head of the market when the fiasco was resolved.

And the moral of the tale? If you want to bet on something be aware of the rules, terms and conditions of what you are betting on. Put another way, if you dance in the dark you're likely to hurt yourself. Especially if you're performing the Quickstep!

Professor Leighton Vaughan Williams is the Director of the Political Forecasting Unit and Betting Research Unit of Nottingham Business School, Nottingham Trent University