Any would-be bank robber who does the math will find another line of work, argue three economists granted access to a confidential data set kept by the British Bankers' Association.

In what's billed as the first cost-benefit analysis of such crimes, the authors note that Britain saw 106 attempted or successful robberies of 10,500 branch banks in 2007. The average haul was $31,600, including the one-third of attempts that came up empty. The average "successful" heist landed about $46,600 — but about 20% of those successes...