Let it be said of happiness economists in years to come: “This was their finest hour.” Just as pilots have scrambled their warplanes at other moments of national crisis, well-being experts must now rev up their regression equations to help us cope cheerfully with the stalling economy. What better time to prove the usefulness of their theories than when financial pain is hitting millions?

Jeremy Bentham, the philosopher, postulated that society should strive for the greatest happiness for the greatest number of people. That idea has underpinned efforts to raise national and individual wealth. Cash looked like a sensible proxy for evanescent happiness.