On October 13 2008 – a public holiday in the US – the Treasury Secretary of the day, Henry “Hank” Paulson, summoned bank bosses to a meeting and made them an offer they couldn't refuse: $125bn of taxpayers' money in exchange for equity in nine US banks. Some banks, such as Citigroup and JP Morgan, received as much as $25bn each. The Treasury also guaranteed new issues of bank debt. It was a bail-out of enormous value to bank shareholders and bondholders, so it can hardly be a surprise that the Obama administration is planning to try to get the money back with some kind of levy.

But how much did the banks benefit from Hank Paulson's “gift”? Did the policy have the desired effect? If so, why? All these questions are answered in research carried out by Pietro Veronesi and Luigi Zingales, economists at the University of Chicago, updated last month. One fascinating conclusion is that Paulson, a former chief executive of Goldman Sachs, may have missed a huge money-making opportunity.

The plan apparently stabilised the financial system in the short run; in the long run, it may have the opposite effect by encouraging some future generation of bankers to take more risks. Both these effects are impossible to quantify.