Incentives matter: sperm file

Daniel Hamermesh at the Freakonomics blog points out

There’s a shortage of sperm in Britain! Apparently, Britain needs donations for about 4,000 women per year; to reach that number, about 500 sperm donors per year are required, while only 300 are currently registered. Things were fine until 2005, when a law was enacted allowing children of sperm donors the right to discover the identity of their father at age 18

Laws affect incentives and changes to law can have unintended consequences.