In my book Messy, I spent a chapter discussing similar examples. There was the time the UK government collected data on how many days people had to wait for an appointment when they called their doctor, which is a useful thing to know. But then the government set a target to reduce the average waiting time. Doctors logically responded by refusing to take any advance bookings at all; patients had to phone up every morning and hope they happened to be among the first to get through. Waiting times became, by definition, always less than a day.
