Hi Y'all (getting better at that!)
        Thanks for the comments regarding attrition of coins from circulation.  I
have rummaged around with many of the factors that have been mentioned but
wanted to keep my inquiry to less than 20,00 words!
        The main points so far are that attrition of coins from circulation is
governed by a whole lot more than coins being dropped down the privy or
otherwise into the archaeological record.
        The US Mint calls in tons of coins each year, but they are noted in their
accounts only by denomination and not by the age of the coin.
        As many have pointed out the time or time frame of the sampling can play a
big role in the outcome: 1950s could have stuff of great age as there
hadn't been much change (pardon the pun) in years, but 1995 had no silver
and wheat pennies as they were "collectable" and were withdrawn form
circulation, also times of economic stress would have forced people to hold
on to hard currency and thus slow down the rate of attrition into the
archaeological record (except as a hoard).
        Then, back to the original question of non-US coins, how do they factor
into some of our contexts?  When I worked for Starbuck at Rogers Island we
found coins of the 1720s to 1750s in the French and Indian War contexts and
most were English, but some were Spanish, and others were counterfiet - how
do you factor in that?  It takes a few months for new pennies to show up at
the lunch counter and long distance travel and access to supply of coins
(ours today is like at no other time in history) would be an overwhelming
factor in attrition.
        Is the "rate" of attrition of coins from circulation something that is too
complex to apply to a broad range of archaeological circumstances?  Must it
be done on a case-by-case or temporally / spatially sensitive basis?  Is it
something that we can work on to at least get some good working models?
How do we do it? (calculating presence in circulation it was simple and
straight forward with visible results, but factoring production boluxed the
whole thing up without much pattern arising).
 
        This will eventually lead on to my next question regading the use of mean
manufacture dates (the mean date of our apartment assemblage indicates that
Jen and I live in the 1940s!)
Don't address this yet - save it for a little later!
 
        Dan W.