PPM Gives False Sense of Security About Counterfeiting

In his article in CN December 2024 Antti Heinonen reported that the majority of central banks which publish data on counterfeiting use parts per million (ppm) as a metric. Due to its relative ubiquity (and the absence of anything better), ppm serves as a useful means of comparing trends both within and between countries. But as a metric it has its shortcomings. This article examines some of those shortcomings and proposes an alternative method based on the number of banknotes used for cash transactions.