US Election First Debate: How Betfair odds moved during previous showdowns

In keeping with what is now US election tradition, money is pouring into Betfair's Next President market in the build-up to tonight's opening TV debate. Over £5.5M has been matched on the main market since Saturday morning and that total volume is expected to break the £100M barrier over the next 24 hours.

At this stage, those betting signals read positively for Joe Biden. He shortened from 1.845/6 on Saturday to 1.784/5 this morning, implying a 57% chance - his highest rating of September to date. Whether that momentum is still intact tomorrow rather depends on his performance tonight.

These debates are real set-piece moments for viewers outside the State, they're streamed live on UK news channels and thus tend to be the moment when our audiences begin to take a much closer interest in the election. Instant impressions are formed and in some part they feed through to the market. Here's what happened in previous cycles.

2004: Kerry odds crash

This was the first US election after Betfair's inception. Going into the debate on 30th September, Democrat candidate John Kerry hit his highest price since February at 3.01201/100. Bettors, it seemed, fancied Bush to have his measure.

That trajectory didn't last. Within 24 hours, Kerry was down to 2.81181/100 and by the second debate nine days later, he was a 2.41141/100 chance. The damaging talking point coming out of the opener was a theory that Bush was receiving instructions from a hidden earpiece.

2008: Obama confirms his supremacy

Barack Obama was already a strong favourite, trading at 1.574/7 on the morning of 26th September. By the next day he was down to 1.538/15 and that was the last time such odds would be seen again. By the second debate, he was a 1.330/100 chance to beat John McCain.

This wasn't an especially dramatic debate. The most logical explanation for the move is that doubts lingered about Obama - still a rookie as merely the junior Senator for Illinois. Would he be bossed around by the veteran McCain? That didn't turn out to be the case and favourite backers quickly took the hint.

2012: Defeat sparks Obama re-election worries

No cycle better illustrates the impact of debates than 2012. They provided the big talking points of the campaign and considerably altered the market. Going into the 3rd October, Obama was trading at just 1.251/4 to win a second term. He was comfortably bettered by Mitt Romney in a famously lacklustre performance.

Within 24 hours, he'd drifted to 1.364/11. By the second debate, 1.491/2. Although he was judged to perform much better in the second debate, the price held. Only after the third did his odds begin to fall further, when it seemed certain the Romney bounce had dissipated.

2016: Bettors give Clinton a big endorsement

At this equivalent stage of 2016, nobody really knew what to expect. Donald Trump had won the Republican nomination despite breaking every debate rule in the book. Their anarchic primary brawls were like nothing US politics had ever seen. How would this 'Marmite' character, an amateur, fare against the seasoned, qualified, yet cold and and in many eyes corrupt, Hillary Clinton?

Going into 26th September, she was trading at 1.68/13. Almost immediately after the debate started, as bettors compared these very different rivals head-to-head for the first time, Clinton's odds crashed. Within 24 hours her odds were 1.4840/85 and they continued to shorten for several days.

By the second debate - an extremely bitter and surreal affair in the aftermath of the 'Access Hollywood' tapes being released - she was a 1.271/4 chance. That fell further to 1.211/5 following the final debate. Polls recorded her the clear winner of all three.

Can we draw any lessons from this relatively small sample? Well clearly, market moves after the first debate are not a good guide to the result. Three of the four movers ended up losing and the winner, Obama, was with hindsight always on course for an easy win.

Also note that the Democrat candidate shortened in three out of the four. In the exception, Obama drifted from a prohibitive mark in response to a universally acknowledged bad night. UK and European viewers were much likelier to support each of those Democrats, so perhaps there's an element of partisanship or confirmation bias in play?

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