If you think I am being unduly cynical, remember that Mr Brown agrees with me about politicians' incentives. In 1997, he accepted what was by then international policy orthodoxy by making the Bank of England independent to set interest rates. The rationale for central bank independence is that politicians cannot be trusted to set interest rates in the nation's interests rather than their own. They will too often give in to the temptation to create a pre-election boom by setting interest rates lower than they should be. If politicians succumb to this temptation in monetary policy, why should we imagine they are
immune to it in fiscal policy?

This self-interest hypothesis helps to explain the absurdity of the pro-stimulation rhetoric. Where we should get a serious attempt at weighing costs and benefits, we get outrageous exaggeration instead.

For example, Barack Obama has promised to do "whatever it takes" to avoid a deep recession. This is apparently the kind of thing people like to hear, but it is preposterous. Doing whatever it takes - in other words, bearing any cost - to avoid a deep recession would make sense only if nothing could be worse.

If an asteroid were on course to obliterate the Earth and all its inhabitants, it would be worth any cost to prevent it. But, short of such a cosmic calamity, nothing is worth any cost to avoid. Perhaps this is why, in an article in the Spectator recommending stimulation, Nancy Dell'Olio went cosmic, claiming that we are being "sucked into the black-hole of a super recession". Few stimulators are as comfortable with cosmic exaggeration as Mr Obama and Ms Dell'Olio, an ex-girlfriend of the former England football coach Sven-Goran Eriksson. Most prefer historical exaggeration, relentlessly invoking the Great Depression of the 1930s. Things could get that bad! We need a new New Deal!

A little perspective is required. During the Great Depression, the gross domestic product (GDP) of the US fell by almost one-third and unemployment reached 25 per cent. In the past six months, US GDP has contracted by less than 1 per cent and unemployment has risen to 6.5 per cent. Perhaps, without stimulation, unemployment would more than triple and the current rate of economic contraction would continue, unabated for 17 years, but it seems unlikely. I have seen no analysis that suggests anything like it.

And, even if this very unlikely reduction in GDP did occur, we would still not experience a repeat of the Great Depression. For we are starting from a position of greater wealth. During the Great Depression, US per capita GDP fell from about $7,800 to about $5,500 (in 2008 dollars). A 30 per cent decline today would result in per capita US GDP of $32,000 - which is higher than Italy's is now.