The Stranger With Your Card Number - scoring a payment in a moment, and why most alerts are wrong

A crowd of well people with one sick person in it, a test that is right 99 percent of the time, and the pile of positive results, which is mostly well people. That crowd is a card network on an ordinary day, and the sick person is the one payment in about six hundred that a stranger made with your number.

Before you start. From Push, Pull and the Instant Transfer - batch rails, instant rails, and who can be tricked: a card payment is a pull, so a stranger holding your card details can start one, and the protection is the right to dispute it. From The Hold That Is Not Money Yet - authorisation, capture, clearing, settlement and chargebacks: a shop asks for permission before the money moves. The 99 Percent Test That Is Usually Wrong is the same arithmetic in a hospital; read it first if “base rate” is new, because this lesson is that lesson with a payment instead of a patient.