Subject: Loop of the Week

Posted by Peter Welles on 11/6/2003
In Reply To:Loop of the Week Posted by John Sterman on 11/5/2003

Message:

Should the water cycle be represented as a closed system in 7th grade textbooks? Should the water in the ocean be included in a good system dynamics model? How about icebergs? Coriolis effects? Should educators make a special effort to identify closed systems in an effort to counter all-too-pervasive linear thinking? Should we really represent the Earth as finite and closed, given the existence of intangibles such as creativity and innovation?

These interesting questions, I think, all rely on an overall question:

What is a barometer I can use for determining how good my model is?
(or more specifically, how do I determine what to explicitly represent in a
model?)

I'll propose the following: utility.

If the model is useful for achieving a certain objective, then it is a good model. What I haven't seen so far in this discussion, however, is an explicitly stated objective, so determining what approach is good for achieving that objective is going to be difficult.

I can easily imagine that a process (like a water cycle) could be usefully represented in many different ways, given different objectives. It seems that a model designed to teach 7th graders about the water cycle (in the sense that "cycle" is defined in most biology texts) would look pretty different than a model designed by NASA to help nations understand the causes and impacts of the long-term variations in the climate system. NASA would not likely find much use in the approach designed for a 7th grade biology textbook. Likewise, NASA's model would probably have very little utility in a 7th grade classroom.

Peter Welles


High Performance Systems, Inc.
46 Centerra Pkwy, Suite 200
Lebanon, NH 03766-1487
Tel. 603-643-9636 - Fax. 603-643-9502 - http://www.hps-inc.com

Follow Ups:

Loop of the Week - Richard Turnock 11/7/2003 
Loop of the Week - Dexter Chapin 11/7/2003