Dana Meadows and prediction

[sbyers@wirb.com]

John Sterman (MIT Sloan) tells us there are two kinds of 
models.  Optimization models do not tell you what will 
happen in a certain situation.  Instead they tell you what
to do in order to make the best of the situation. The
purpose of a simulation model, on the other hand, is to 
mimic a real system so that its behavior can be studied.
Optimization models are prescriptive, but simulation models
are descriptive.  That is, simulation models are "what if"
tools.  Often such "what if" information is more important 
than knowledge of the optimal decision.  (The preceding is
taken directly from a paper by Dr. Sterman, titled "A
Skeptic's Guide to Computer Models, 1991.  If you are an
amateur, such as myself, you can read this paper and be
confident that you now know some correct things about models
and their lmitations.  Dr. Dana Meadows has three works
cited.)

This is certainly how Dr. Dana Meadows thought, as well.
"Limits to Growth" (all three editions) is not about
predicting anything. Perhaps there was criticism because
many people do not understand the purpose of modeling
systems.  The model described in "Limits to Growth" 
certainly evolved as the modelers learned, but they never
claimed to predict a thing.

Steve Byers


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