US election betting: Bets are everywhere but are they right?

Betting markets, which have a long history outside the US, have been wrong before: they heavily discounted the odds of a Trump victory in 2016, for example, and thought Republicans would fare better in the 2022 midterms than they did.

But academics say the markets tend to be useful forecasting tools.

Still, Prof Gruca said the public should be sceptical of some of the platforms, noting they don’t have a track record and could be subject to manipulation, given the huge sums of money involved and the risk that the pool of participants is not deep enough to match all bets.

“When you don’t have limits, then it is the deep pockets which moves the prices,” he said. “Your opinion is weighted by the size of your cheque book.”

On Polymarket, for example, big bets from four accounts controlled by a French trader helped to tilt the odds for Trump earlier this autumn.

Researchers have also told reporters they have seen signs on Polymarket of wash trading – that the same people are buying and selling repeatedly, giving the illusion of more activity than there actually is.

Polymarket – which allows users to bet against each other on a specific future outcome and unusually operates using crypto – did not respond to a request for comment from the BBC.

Its chief executive, Shayne Coplan, has previously called the platform a “reality check” and “much-needed alternative data source”, noting that it correctly forecasted that President Joe Biden would drop out of the race.