i heard a lecture recently, in which someone mentioned a small experiment, where he tallied the dates of the coins in the pockets of his acquaintances, and i was wondering if anyone has seen reference to anything more systematic? i know philip barker makes reference to the problems of trying to date the contents of someone's pockets based on the coins he tried to use to make a phone call, but i was wondering if there might have been a more systematic study done somewhere, sometime, and not necessarily by archaeologists (banks or mints, to guage the age of coins in circulation?)