Re: Swarmfest 2000 Call for Participation and Papers

[M. Lang & S. Railsback]

Hi Irene:

It looks like I'll be able to attend SwarmFest. If possible I would like
to present the following talk. I think 20 minutes would be enough time
for it.

Thanks very much.

Steve Railsback

Title: Getting "Results": The Pattern-oriented Approach to Analyzing
Complex Systems with Agent-based Models

Preliminary abstract: A critical question commonly heard by Swarm
modelers is whether agent-based models can produce "results"- general
concepts instead of just noisy stochastic simulation output. This
question results largely from the very questionable assumption that
conventional differential equation models are more general because they
use aggregated measures of the population being modeled, but this issue
still must be addressed by agent-based modelers. Pattern-oriented
modeling is a framework for ecological analysis but is widely applicable
to complex systems. This approach involves designing a model
specifically to simulate observed patterns of system-level behavior, and
testing the model by whether it can reproduce those patterns.
Alternative formulations for agent behavior can be posited as hypotheses
and tested by whether they reproduce observed system-level response
patterns. This provides a hypothesis-testing approach that allows
inferences about agent behavior. We applied this approach to a model of
how fish select habitat in a stream. The model was designed to predict
how individual fish select among alternative habitats that vary in food
intake and mortality risks. From the fish literature, we a priori
identified six patterns of observed habitat shifts in response to known
stimuli, then tested the model to see if these patterns emerged from
individual behaviors. Three alternative rules for making habitat choices
were compared, and two of the rules were rejected as unable to reproduce
the observed patterns. This analysis produced "results": we showed that
some assumptions commonly made by ecologists are incapable of explaining
population-level patterns.

-- 
address@hidden
Lang, Railsback & Assoc.
250 California Ave., Arcata CA 95521
707-822-0453; Fax 822-1868


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