One hallway is crammed with photographs signed by celebrity pals: Robert De Niro, Kevin Costner, Madonna, as well as Tiger Woods, James Brown and a Miss World or two.

The study was carried out by academics Rose McDermott at Brown University, James Fowler at the University of California and Nicholas Christakis at Harvard.

Mr Brown did not invoke the name of James Tobin, the economist who proposed a levy on currency dealings in the 1970s.