What lessons can we learn from last time?
At 1.05am EST on November 3rd 2004 the US news channel, CNN, showed the above graphic on the screen illustrating the result of an exit poll in Ohio, the key state that Senator John Kerry had to win if he was to beat George W. Bush for the Presidency.
The message was clear. Kerry was ahead in Ohio and the chances were that the state would give him enough votes in the electoral college to become the next President. The exit polls and the leaks about them the previous evening had completely turned the White House Race betting market on its head.
When the polling stations had opened on the day before Bush was an odds on favourite to win. By the time the exit polls had been published things had changed dramatically. Those few hours saw the biggest political gambling spree ever seen with an estimated Â£25m being bet in the UK alone.
The exit poll results had been produced for a consortium of the major US news organizations, working as the National Election Pool (NEP). They were based on interviews with voters in 49 states. In the days and months that followed there were huge investigation into why the NEP figures, particularly in key states such as Ohio, has been wrong.
The co-director of NEP, Warren Mitofsky, was quoted as saying â€œthe Kerry voters were more anxious to participate in our exit polls than the Bush votersâ€. Another suggestion was that women, who were marginally more pro-Kerry and certainly in the early polls they represented 58% of the sampled voters.
Whatever the post-elections explanations this was completely irrelevant to the betting. Punters were making decisions in an instant and the conclusion from what was being reported about the polls was that Kerry had won. Many gamblers lost a lot of money that night and one of the bosses of a spread-betting company told me later that it was one of their most profitable sessions ever.