I would like to suggest that perhaps it is partly Geoff Coyles use of
the term "rate-dependent rates" that is confusing people. I may be
wrong but I dont believe you will find the term "rate-dependent rates"
in any of Dr. Forresters works. Certainly he does (and does it very
clearly as usual) prohibit the writing of rate equations that include
another rate and he also, I believe, mentions that in a diagram no rate
can connect directly to another rate. And I think he says that the only
inputs to rates can be levels (with the minor quibble that auxiliaries
can also feed into rates -- minor because proper auxiliaries can always
be completely eliminated by including them in the rate equation they
feed into.) And Im sure that he mentions many times that rates and
levels must alternate.
As silly as it seems, perhaps if Mr. Coyle had used a phrase such as
"rates that depend directly upon other rates" there would have been less
chance of confusion. Then, however, if people who claim to be using
system dynamics still are confused about this concept, then Im as
appalled as he.
John W. Gunkler
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