Here are my random thoughts...
In order to study the real effects of policy changes one needs to get the
response variability of the model system to the same level than the real
system. Therefore, you need the right level of heterogeneity of the agents
but also a scale model would help to account for unforeseen effects that you
do not model explicitly, at least that is my experience. Often the size of
the modelled population regulates the effects of policy changes. It is also
important to remember that a group is not just a collection of individuals
but develops its own dynamics. These might be different for different group
sizes. Bigger groups might create additional dynamics and consequently the
levels of variability and stochasticity within the simulation model will
change even if the proportions of stereotypes within the groups are kept
constant (is that what people often call emergence?). Therefore, I think,
size matters!
Another aspect to consider is validation. Previously I initiated a SIMSOC
discussion about validation of ABMS models. From there I learned that AMBS
models are often validated quantitatively on a micro level and qualitatively
on a macro level (see for example Moss and Edmonds, 2005). I guess that
having a scale model of the real system definitely supports the qualitative
validation on a macro level and might even allow some (limited) form of
quantitative validation on the macro level.
Regards
Peer-Olaf
Reference:
Moss, S. and Edmonds B. (2005). Sociology and simulation: statistical and
qualitative cross-validation. American Journal of Sociology 110:1095-1131.
--
Dr. Peer-Olaf Siebers
Research Fellow
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Intelligent Modelling and Analysis Group (IMA)
School of Computer Science
University of Nottingham, UK
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Phone: +44(0) 11584 67666
Website: http://www.cs.nott.ac.uk/~pos/
On Sun, 10 Aug 2008 22:17:32 +0100, Nigel Gilbert <[log in to unmask]>
wrote:
>In what circumstances might it be necessary to implement agent-based models
>of thousands or millions of agents, rather than the more typical tens or
>hundreds? Do you know of any examples where scaling up the model (in terms
>of the number of agents) gives qualitatively different results? Do you know
>of any literature that addresses this issue?
>
>
>Iąd be very interested to hear of any suggestions.
>
>Thank you,
>
>Nigel
>
>
>_______________________________________________________________________
>Professor Nigel Gilbert, Editor, Journal of Artificial Societies and
> Social Simulation, <http://www.soc.surrey.ac.uk/JASSS/>
> Centre for Research on Social Simulation (CRESS)
> Department of Sociology, University of Surrey, Guildford, UK.
> Tel:+44 1483 689173 [log in to unmask]
> <http://cress.soc.surrey.ac.uk/>
>
>
>
>
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