I've always treasured a crack by Rose Friedman about the illusion of precision in economics. Her husband Milton was half-way through declaring that if you can't measure something you don't really understand it when she interrupted with "If you can't measure it, measure it anyway". Which brings me to Michael Ignatieff's latest swaggering statement that he and his party will support the Tory budget provided they get quarterly updates including how many jobs it is creating. The trouble is, you can only know how many jobs it created if you know exactly what would have happened in employment markets if the budget had been different or absent. And since we can't run history two different ways we can't even if we have really fast computers that let us pretend we've somehow created a spreadsheet that completely accurately captures every interrelationship in the economy and accounts for chance as well. (To test this proposition, plug 1980 data into the spreadsheet and see if it predicts 1985.) On the plus side, this approach lets talking heads sound wise and politicians talk tough while acting weak. If you think that's good.