Drain or gain?

WHEN people in rich countries worry about migration, they tend to think of low-paid incomers who compete for jobs as construction workers, dishwashers or farmhands. When people in developing countries worry about migration, they are usually concerned at the prospect of their best and brightest decamping to Silicon Valley or to hospitals and universities in the developed world. These are the kind of workers that countries like Britain, Canada and Australia try to attract by using immigration rules that privilege college graduates.