Every market capitalisation league table tells a story. Look at the market cap numbers for banks and you may think that you are seeing double. In fact, you are, but don't go to the doctor or book yourself a suite in the nearest drying-out clinic.

The market value of Citigroup is actually slightly more than double its nearest competitor, HSBC Holdings, at $255bn versus $108bn. If that comparison doesn't make you wobble on your bar stool, Citigroup is four times larger than UBS, five times Barclays and six times Deutsche.