I guess that an agent-based modeling tool can easily emulate (or, possibly,
include --- see http://jasss.soc.surrey.ac.uk/4/3/1.html) a system dynamics
model, but a system dynamics modelling tool will have some difficulties to
emulate an agent-based model, so perhaps agents CAN cover all the world (see
http://www.uni-koblenz.de/~kgt/Pub/Cortona5.pdf)!
And as for "top-down": I don't think SD goes "down" to the level of
individuals, so in some way, it stays on top (or better: on the surface
...).
Best regards
Klaus G. Troitzsch
--------------------------------------------------------------------
Prof. Dr. Klaus G. Troitzsch
Institut für Wirtschafts- und Verwaltungsinformatik
Universität Koblenz-Landau
e-mail: [log in to unmask]
www: http://www.uni-koblenz.de/~kgt
-----Original Message-----
From: News and discussion about computer simulation in the social sciences
[mailto:[log in to unmask]] On Behalf Of Cesar E Garcia Diaz
Sent: Monday, January 08, 2007 7:40 PM
To: [log in to unmask]
Subject: Re: System dynamics
...
I am not defending SD. It is just that I do not think that AB is the "master
tool" to always study social systems and emergence, same as linear
programming is not the master tool to solve any optimization problem.
All the best,
Cesar
Scott Moss wrote:
> All of the responses so far to my posting seem to me to raise
> interesting and valid points. Some years ago on this list we had a
> long discussion about modelling top-down or bottom-up. The modelling
> elements of that discussion were reported as a symposium among Rosaria
> Conte, Bruce Edmonds, myself and Malcolm Sawyer in CMOT. I don't want
> to revisit the same discussion.
>
> So can we stipulate that SD is a sort of top-down modelling approach
> with a static representation of social structure and no direct
> representation of interaction among socially embedded individuals?
>
> Nearly 10 years ago, Van Parunak demonstrated that for a particular
> social target an SD model yielded different results from those of an
> agent based model. As I remember, Van ascribed the difference to the
> effect of agent interaction.
>
> I am not aware of any general results in this vein.
>
> If the result were general, then we could define the domain of
> application of SD social models as the set (or a subset) of cases
> where social interaction among individuals does not affect the macro
> level outcome. Similarly, the domain of application of agent based
> models would be where social interaction does affect macro level outcomes.
>
> If it is possible to capture agent-based macro level results with an
> SD model, then there might well be efficiency gains in using such a
> model where scaling up the number of agents is computationally too
> expensive with available technology. For this to be a reliable
> procedure, we would need some general results about -- or experience
> with -- the conditions in which macro level outcomes can be
> represented as if they did not emerge from social interaction.
>
> What is not true is the remark that stimulated my original posting.
> It is false to say that system dynamics is the modelling method of
> choice for social systems. You can only have confidence in its
> applicability where there is no effective social interaction among
> individuals and the social structure is static.
>
>
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