Re: Modeling the Emergence of Political Parties

[M. Lang / S. Railsback]

Paul Johnson wrote:
> 
> "glen e. p. ropella" wrote:
> >
> > Be careful saying stuff
> > like "With simulation, the problem is that we often have no clear
> > notion of what a result is..."

Ok, I'm jumping in with my hypothesis:

I think when some scientists do a derivation or "proof" with
differential equations, they think they've discovered a result that is
universal. On the other hand, when they see a simulation model result,
they consider it one data point for one special set of circumstances.

What the differential equation modelers forget, however, is all the
assumptions that went into their "proof" and how valid they are ... and
if they really restricted themselves to situations where their
assumptions were valid, they'd be down to about one data point too.

So the question is- how can we design sets of simulations that would
convince the old guard that the simulation results demonstrate a general
principal instead of one special case.

I'm in the middle of simulations to "test" a rule for letting fish
decide where to move among habitats with varying mortality risks and
food intakes. There's an old rule (move to where the ratio of
risk/intake is lowest) that was mathematically derived and therefore
assumed of universal applicability, even though the derivation was a
very specific set of special circumstances that are not even remotely
similar to those in the models. We designed at set of simulations
similar to Darren's approach, showing that our model reproduces a number
of well-established patterns of behavior (and other rules do not). In
the process we're finding examples where the derived movement rule
results in decisions that are very unrealistic. I'm hoping that this set
of simulations will be accepted as a "result"- that our approach to
modeling habitat selection apppears generally applicable whereas others
do not. We'll see.

I know in ecology people are also reluctant to accept simulation output
as real "results" because there is a long history of poor computer
science practices. (I know I never believe a simulation paper unless
there's discussion of how the model and its code were tested, and such
papers are mighty mighty rare.) But somehow its a lot easier to ignore
the uncertainties in a differential equations model.

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


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