Every government minister, senior civil servant or charity official is familiar with the pitch. Spend money on my project, says the supplicant: it will bring such large benefits that you will actually save money in the long run. At this, the official sighs, knowing that another supplicant with an equally bold pitch is waiting outside. How can he pick among competing pleas for bridges, IT systems, deworming medicines and a thousand other things? This week, at a conference in Dhaka, the Copenhagen Consensus will try to answer that question, reports the Economist.