And there is a new series of experimental statistics that aims to capture labour market flows.

BBC: Go Figure: How likely are you to lose your job?

Sadly for Labour, this is an experimental proposition that cannot be tested: Mr Cameron inherited coffers that are empty, not full.

ECONOMIST: Bagehot

On the other hand, an experimental police project in Catford, south London, has shown that Labour's plans for curfews are unnecessary, since more carefully targeted restraints can already be imposed under existing laws.

ECONOMIST: Young offenders