The chances of President Donald Trump being impeached before the end of his first term have been hovering around fifty percent for months.

And although the odds of Trump’s impeachment have been a source of conversation even before he was sworn into office, it’s been unclear how the political betting site, Ladbrokes, has been calculated the odds it makes on the event.

But Matthew Shaddick, head of political betting at London-based Ladbrokes, tells Inverse that the odds are built by the wisdom of the bettors, balanced by his professional opinion, and altered by changes in the overall political climate. The nearly 50 percent chance of Trump’s impeachment is remarkable, he says.

“I personally think it’s very optimistic of people to bet that he’ll be replaced within four years,” Shaddick says. “There’s a two of three percent chance of it happening.”

It’s illegal in the United States to bet on the outcome of political races, unless you’re taking place in some sort of prediction market. This means that the popular “Donald Trump Impeachment Odds” special running on Ladbrokes features bets exclusively from bettors who are not in America.

Ladbrokes Donald Trump impeachment odds
These are the current odds on Ladbrokes on Donald Trump's impeachment.  Shaddick said the Nobel Peace Prize odds were 100/1 a week ago.

Ladbrokes is a betting company, so it is still trying to make money on the odds it runs, and it uses the experience of its oddsmakers to try and stay on the profitable side of that spectrum, explains Shaddick. “We usually have an outcome that will make us money and an outcome that will lose us money,” he says. “We simply hope that the amount of money we pay out on winning bets is less than we take in on total bets.” To do that, the company relies on its forecasters to judge what the smart outcome will be, and use that to create betting scenarios.

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“I have a background in political science, but I joined Ladbrokes because I knew a lot about horse racing at the time,” says Shaddick. This expertise has led Shaddick to be one of the few political betting experts employed full time, and what Ladbrokes is depending on when running political specials. The key to the odds is a level of impartiality — for elections, he relies on statistical models like Nate Silver’s *Five Thirty Eight.

Without statistical models, the first thing Shaddick did to set Trump’s impeachment odds was look at the historical precedent. With just Nixon being forced to resign due to impeachment, out of 44 previous presidents, he ended up with pretty low odds. He then factored in the Republican-controlled Congress, and the number of presidents that only served a single term. He ended up thinking the real chances were about two to three percent that Trump would be impeached. He says, “for the market to say there’s close to a fifty percent chance of that happening is incredible.”

“There’s reason to think that the betting market might not be a perfect representation of the actual possibility,” says Shaddick. He’s seen bettors in the UK become more predisposed to bet on the populist option, or on political upheaval since Brexit and Trump’s election. On top of that, options that offer money sooner tend to be more popular with bettors. He says, “in these long-term betting odds, they often skew towards the short term.”

Because of this, and since Shaddick thinks Trump’s impeachment is pretty unlikely, the company has held the betting odds close to even, despite getting five or six times more action on the possibility of Trump getting impeached, at a rate of a few thousand pounds a week. “I know he’s unusual,” he says. “I think people are getting a bit too carried away with the possibility of him being replaced.”

There was nothing like this during President Barack Obama’s terms, Shaddick says, which he says shows just how unusual the situation is. Right now he doesn’t see the odds changing — but he says that the odds can always change, especially because he’s watching the news carefully for hints.

“Some extra story is going to have to come out about Russian connections [or something similar],” he says. “If people really think this is going to happen the odds are going to change extremely quickly.”

Photos via Ladbrokes, Getty Images / Pool

Dyani Sabin is a science writer from small-town Ohio transplanted to New York City. Former biology researcher and library supervisor, you can also find her writing at Scienceline. Email her at dyani.sabin@inverse.com