It is bank bonus season, seven years on from the greatest financial crisis for generations, and size still matters. Investment bankers — and their critics outside the sector — continue to obsess about how much they are paid, while largely ignoring a much more important question: do cash bonuses even work?

John Cryan, Deutsche Bank’s co-chief executive, seems not to think so. Claiming to be perplexed about the bonus clause in his contract, he told a conference last year he would “not work any harder or any less hard in any year, in any day because someone is going to pay me more or less”. It was an echo of outgoing Shell boss Jeroen van der Veer’s comment in 2009: “If I had been paid 50 per cent more, I would not have done [my job] better. If I had been paid 50 per cent less, then I would not have done it worse.”

The impact of a cash bonus is often shortlived. Staff quickly start to think of it as a permanent part of their compensation. The following year they quite naturally become upset if their bonus turns out to be lower.