Britain's pedophile-phobia has reached new heights of insanity — now everyone who comes into contact with a child at school has to have a police background check and get certified as genuine non-pedophiles. But not just once — over and over again; a different certificate for teaching karate, escorting field trips, or giving a presentation on careers day. Because, you know, you might not be a karate-teaching pedo, but you might be a field-trip pedo. Everyone's included from Members of Parliament to authors giving a reading. Charlie Stross has some good commentary on the potential dangers all this background checking creates:
As you can imagine, the authors are upset. As Philip Pullman puts it, "It seems to be fuelled by the same combination of prurience, sexual fear and cold political calculation," the author of the bestselling His Dark Materials trilogy said today. "When you go into a school as an author or an illustrator you talk to a class at a time or else to the whole school. How on earth — how on earth — how in the world is anybody going to rape or assault a child in those circumstances? It's preposterous…"
Even the simplest of databases have been found to contain error rates of 10%. (The HMRC database in this study contains merely first, second and surname, title, sex, data of birth, address and National Insurance number — nevertheless 10% of the records contain errors.) Other agencies are even more prone to mistakes. For example: my wife recently discovered that our GP's medical records showed her as having been born outside the UK rather than in an NHS hospital in Manchester. We don't know why that error's in the system, and we've got the birth certificate and witnesses to prove that it is an error, but imagine the fun that might ensue if the control freaks in Whitehall decided to enforce record sharing between the NHS and the Immigration Agency …! (Hopefully they're not that stupid, but who can tell?)
The point is, if 10% of government database records contain an error, than the probability of a sweep of databases coming up with an error rises as you consult more sources. And there are a whole bundle of wonderful ways for errors to show up. If your name and date of birth are the same as someone with heavy criminal record, a CRB check could label you as a bad guy. If your social security number is one digit transposition away from $BAD_GUY, see above. If the previous owner of your house was a child abuser, see above. If your street address is one letter/digit away from a street address occupied by a criminal and some bored clerk mis-typed it, you can end up being conflated with somebody else. And the more sources the CRB checks, the higher the probability of a false positive result — that is, of them obtaining a positive result (subject is a criminal) when in fact the subject is a negative.
This is not a hypothetical worry. As of last November, the CRB had falsely identified more than 12,000 people as criminals, according to the Home Office. (Raw parliamentary answer here.) These are the disputes that were upheld, that is, ones where the falsely mis-identified were able to convince the CRB that their record was incorrect. These are false positives which have been conclusively identified as such. While the identified false positive rate is around 0.1%, the true figure is certainly much higher: because there will be a proportion of individuals identified as false positives who are in the unfortunate position of lacking the documentation to prove their innocence.