If you've got lucky, it's easy to convince people you're a sage

"Expert" predictions only need a few lucky guesses, then everyone believes them.

LSE's Nattavudh Powdthavee and Nanyang University's Yohanes E. Riyanto presented a paper last month titled Why Do People Pay for Useless Advice? (pdf) The authors demonstrate that people are prepared to pay for investment advice which they know cannot possibly be based on any real evidence – provided the advisor has got things right in the past.

Participants in the experiment were told to bet on five consecutive rounds of coin flips (they could pick the stake, provided it was higher than a minimum level and wouldn't make them lose all their money before the last round). Since they were using a fair coin, the chance of heads or tails coming up each time was 50-50, and the chance of someone calling the correct flips in all five rounds is one in thirty two. More importantly, no amount of expertise can help one predict the outcome of a sequence of coin tosses.

So when the participants were offered the chance to buy "predictions", you would expect them to ignore them. And most of them did, at least for round one (although even then, around 15 per cent of them did pay). But after the first round of tosses, everyone got to see their predictions, even those who hadn't paid. And for half the participants, those predictions were correct. Still, it's obviously just chance, right?

Apparently not so obvious. Those who got a correct "prediction" in round one were three times more likely to pay for one in round two than those who'd got an incorrect one. And by the time a subset of the group had got four correct predictions in a row, the possibility that they would buy a prediction for the fifth round had risen from 15 to 40 per cent.

In other words, just a few lucky guesses are all it takes to get people to pay for what the authors call "transparently useless advice". As they conclude:

Our experiment accurately describes how the real "false" experts typically operate in the information market, and the findings of this paper help to highlight how easy it is for an average person to form a belief in an expert when none may actually exist. 

Something worth bearing in mind next time you are looking at horse tips, stock pickers, or hedge funds, maybe.

George Bush tosses a coin. Is he an expert? Photograph: Getty Images

Alex Hern is a technology reporter for the Guardian. He was formerly staff writer at the New Statesman. You should follow Alex on Twitter.

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What did Jeremy Corbyn really say about Bin Laden?

He's been critiqued for calling Bin Laden's death a "tragedy". But what did Jeremy Corbyn really say?

Jeremy Corbyn is under fire for describing Bin Laden’s death as a “tragedy” in the Sun, but what did the Labour leadership frontrunner really say?

In remarks made to Press TV, the state-backed Iranian broadcaster, the Islington North MP said:

“This was an assassination attempt, and is yet another tragedy, upon a tragedy, upon a tragedy. The World Trade Center was a tragedy, the attack on Afghanistan was a tragedy, the war in Iraq was a tragedy. Tens of thousands of people have died.”

He also added that it was his preference that Osama Bin Laden be put on trial, a view shared by, among other people, Barack Obama and Boris Johnson.

Although Andy Burnham, one of Corbyn’s rivals for the leadership, will later today claim that “there is everything to play for” in the contest, with “tens of thousands still to vote”, the row is unlikely to harm Corbyn’s chances of becoming Labour leader. 

Stephen Bush is editor of the Staggers, the New Statesman’s political blog.