No, seriously, economists sometimes really do have very good ideas, ideas that can improve society, change lives and save money. Sometimes the wisdom of the idea is so obvious, you wonder why it took an economist to think of it.

Try this: The people and corporations running our prisons should be paid in proportion to the number of their inmates who don't re-offend. That could turn prisons into rehabilitation centres instead of schools for crime, slash recidivism rates and reduce considerable direct and indirect costs of crime - everything from insurance claims to police, courts and victims' expenses, not to mention the very costly business of keeping people in choky and the tendency of prisoners' and their families to be more frequent social welfare customers.

This suggestion, tucked away in the and the blog last week and deserving wider consideration, came from Andrew Leigh, an economist with the Australian National University's Research School of Social Sciences.

According to Leigh, nearly 50 per cent of the 20,000 or so prisoners shown the door this year will end up back inside within two years. Get the profit motive to work though and that could be dramatically altered, particularly if more than the present 16 per cent of inmates were held in appropriately incentivised privately-run jails.