The Guardian – Alex Bellos
“Let’s say that 1 in 10,000 people who present themselves at UK passport control have invalid passports, and let’s say that UK passport control is pretty good at detecting invalid passports. When presented with an invalid passport, an officer will pick this up 99 times out of 100. Travellers found with invalid documents are sent to a holding cell. Let’s also imagine that UK passport control will, out of caution, very occasionally send someone to the holding cell whose passport is perfectly valid. These “false positives” occur just 0.1 per cent of the time.” (more)