We are used to the concept that when a butterfly flaps its wings in Brazil all manner of unspeakable things happen in New Jersey and Tunbridge Wells. But many have struggled to understand the link between Mrs Watanabe's mood swings and the price level of exotic currencies, distant equity markets and sundry commodities. What, in short, does a Japanese housewife have to do with the price of tea in China?

Mrs Watanabe is crude shorthand for Japan's $15,000bn pool of savings, the deepest in the world and worth more than the annual economic output of the US. These vast resources are somewhat apocryphally marshalled by Japanese women, who have traditionally held a firm grip on family finances.