American incomes, measured as wages and salaries, rose almost 4% in the year just passed - but the same Americans have been spending at a rate of almost 7%.

Where has the difference come from? Work it out for yourself: American banks and the US stock markets.

This is a classic example of the way this part of the modern American market economy works.

Individuals earn, invest in shares (more people invest in shares in the US than anywhere else in the world) share prices rise, the investors feel good, so they (i) either borrow to buy more shares, or (ii) borrow to spend because their higher shares make them feel wealthy.

From Europe, it is easy to see Americans as profligate - big boastful spenders with all the latest new toys, computers, cars, what have you, while the rest of the world is more responsible and frugal, and saves.

But American spending is what keeps a large part of the world economy afloat.

Japanese dependence

This is never truer than in the case of Japan. If Americans stopped spending on the goods the Japanese produce, the Japanese economy would be in far worse shape than it is already.

Which makes written remarks last week by the deputy Japanese Minister of Finance, Eisuke Sakakibara, all the more alarming.

Mr Sakakibara criticised the Americans for their lack of savings, saying this would be their downfall.

He could be partly right, of course, because when the crunch comes and Wall Street turns down - as all markets do sooner or later - and the credit dries up, American spenders will lose money, and in some cases, jobs.

Big spenders wanrted

But for now, they are almost single-handedly keeping the world economy going.

Until the Japanese, or Japanese policy-makers, grasp that they are part of a bigger picture, and a wider world, and that they have a responsibility to do their bit, they risk continuing to show, as they have throughout the trials of the last year and more, that they are still shirking their global responsibility.