Subject: Stocks and Flows

Posted by Debra Lyneis on 3/10/2004
In Reply To:Stocks and Flows Posted by Lees Stuntz on 3/2/2004

Message:

Hello All,
It's great to see the listserv revived!

Implicit in every stock/flow diagram is the concept of "time." A stock is an accumulation, like water in a bathtub or money in a bank account. It is expressed in units -- gallons or dollars in these examples.

A flow tells us how that accumulation grows (or decreases) over time. It is expressed in units per time -- gallons/minute and dollars/month.

A population is an accumulation of people. It grows by the flow of births
(people/year) and decreases by the flow of deaths (people/year.) Distance (traveled by a bus, runner, projectile, etc) is an accumulation of miles or feet. It is increased by miles/hour or feet/second. As time elapses, the accumulation grows or decreases.

It may help to explain stocks and flows if you think in terms of the units and how they accumulate over time. Make the role of time explicit in the discussion.

Debra Lyneis
Creative Learning Exchange

Follow Ups:

Stocks and Flows - Steve Puettner 3/10/2004