DNA databases kept by police forces have grown all over the world since Britain launched the first one in 1995. Police in England and Wales have since amassed profiles of 8.7% of the population, by routinely taking samples from everyone arrested. Samples are held for six years. On Tuesday November 24th the author of a government report on DNA databases claimed that the police were making arrests purely to get more samples on file. Three out of four young black men are now said to have their profiles on the database. Yet the usefulness of DNA databases is not apparently related to size. DNA reportedly helped with 58% of criminal investigations in England and Wales in 2008, compared with 70% in Scotland, which destroys samples taken in more minor investigations and so holds profiles of a much smaller share of its population. According to the FBI, California's database, with 1.2m profiles, has aided nearly 8,000 investigations while Florida's, at half the size, has helped in over 10,000 cases.

AP