REPLY Age of material in a stock (SD6434)

[SDMAIL Bill Braun]

Posted by  Bill Braun <bbraun at hlthsys.com>

I understood Jay's question to refer to the aging in a particular stock, 
in other words the "mixing" of items within a single stock. In a number 
of examples offered in response to his question, John's below being a 
good example, I have been asking myself why we are trying to extract 
aging information from a single stock when multiple stocks would reveal 
the same information.

Using John's inventory example, why would I not establish a separate 
stock for each of the policy decision points? So, if I want to 
differentiate the age of inventory in five day increments, I would 
model a stock for [the first] five days, flow its contents into the 
second five days, into the third five days, etc. until I reach an 'X 
days and older' stock. Shipments would draw from the oldest stock 
(FIFO) or the youngest (LIFO) or any other relevant combination. The 
net of all flows would be the inventory in each aging stock. At any 
point in time, the aging of inventory, patients in a queue, time in a 
trail, etc. would be known by the number of people/items in each of 
the aging buckets.

I think this would also suffice for Jack's new medical products scenario, 
as well as Bob's red water example (very helpful, thanks Bob).

This seems simple enough, so simple that I now question my understanding 
of the original question, and the many examples and explanations offered. 
To conceptually quote Bob, I haven't actually tried this in a model, 
which I suppose is as close to a cardinal sin as I can get (that is, 
assuming I can sort this all out in my head).

Bill Braun 
Posted by  Bill Braun <bbraun at hlthsys.com>
posting date  Mon, 23 Apr 2007 15:32:21 -0400