SD Country model

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Anastassios Perdicoulis
Member
Posts: 20
Joined: Fri Mar 29, 2002 3:39 am

SD Country model

Post by Anastassios Perdicoulis »

Hello to Martin, and to all the SD community

The new Environmental Dynamics group (
www.utad.pt/ed)
is handling this sort of models. The model collection
will be launched shortly after the 24th of June, although
I dont think there is any "country"-level model yet.
For more inquiries, please contact me, and shall have
an answer by the end of the month.

Greetings to all,
Tasso Perdicoulis

www.utad.pt/~tasso
tasso@utad.pt
TGAEggers@aol.com
Junior Member
Posts: 3
Joined: Fri Mar 29, 2002 3:39 am

SD Country model

Post by TGAEggers@aol.com »

It appears that this process can only deal with the parts, rather than
systemically hooking the parts together wholistically. On the surface,
(half-baked on my part) it almost seems to defeat the "ideal" of being "part
of," rather than being "apart from" the processual endeavor of systems
dynamics.

Respectfully,
John Eggers
From: TGAEggers@aol.com
Anastassios Perdicoulis
Member
Posts: 20
Joined: Fri Mar 29, 2002 3:39 am

SD Country model

Post by Anastassios Perdicoulis »

Dear Jim,

I have been following your excellent pieces of advice to Martin, and I would
like to ask you two things:

1. Would you be interested in organizing and publishing this advice in the
brand-new modelling site "Environmental Dynamics Vitrine"
(
www.utad.pt/ed/vitrine)? They would fit perfectly under the "Theory"
section.

2. Would you be interested in joining the Editorial Board of the EDV? That
would be an honor to all participants, given your experience and "sense of
community" (i.e. sharing)!

Best regards,
Tasso

---
Anastássios Perdicoúlis
www.utad.pt/~tasso

Jim Hines wrote:

> Martin,
>
> Its good that you are using the "standard method" for each of your
> sectors. But, Im concerned for you about developing the model by
> sectors.
>
> Dividing a model into sectors is a common strategy in SD, but not one
> that always (usually?) works. The problem is that when the modeler
> hooks the sectors together, he will be completing tens, hundreds,
> thousands, even tens of thousands of loops (depending on the size and
> "density" of the model). This means that the modeler can be confronted
> with new, puzzling patterns of behavior at precisely the time the model
> is most difficult to analyze (i.e. when its as big as its going to get).
> The danger is multiplied when different people have developed the
> different sectors (which is usually the whole idea behind dividing it
> into sectors in the first place).
>
> The MIT National model suffered from this approach, I think: A number
> of dissertations (most of which I listed in the prior email) were done
> as new sectors, developed separately from the larger model. The sectors
> themselves were fine pieces of work, but incorporating them into the
> larger model was difficult, as has been understanding the dynamics of
> the National Model, though this is not only due to the early sectoral
> approach -- the National Model really is a complicated model.
>
> People sometimes mistakenly think the sectoral approach will work
> because the approach is lauded in other fields. For example, the
> sectoral approach is used by software developers. But in such fields
> the approach works only because interactions between sectors can be
> minimized (by good developers). Unfortunately in system dynamics, we
> dont want to minimize those interactions -- the interactions are what
> were interested in (otherwise why put the sectors together at all?).
> So, what works in software development and maybe other fields wont
> necessarily work in SD model development.
>
> A better approach, I think, is to apply the "standard method" to the
> real subject of interest -- The economy -- rather than to the
> individual sectors.
>
> The 5000 dollar question remains: How do you make use of a more than one
> person in creating a model, if you DONT rely on a sectoral approach. I
> know of one SD consulting firm that (at one time) could put three people
> on a model -- but in this case only one of the people did the modeling.
> One of the other two people would take charge of the data and the other
> person would take the role of project manager (plus relationship manager
> and coach).
>
> Id be very interested in hearing on this list experiences or
> speculations on how more than one person can participate in modeling.
> (Note: Im mostly interested in approaches that dont rely on sectors,
> but defenders of sectors are welcome to get their licks in (as if I
> could stop you!)).
>
> Jim Hines
> jhines@mit.edu
"Thompson, Jim A-136"
Junior Member
Posts: 7
Joined: Fri Mar 29, 2002 3:39 am

SD Country model

Post by "Thompson, Jim A-136" »

There a searchable bibliography of system dynamics publications available
from
http://www.albany.edu/cpr/sds/biblio/sdbib.html. I understand that
Professor Jay Forrester, who initiated the System Dynamics National Model at
MIT, is writing a book about the model process and content, but I do not
know the anticipated publication date.

If your interest includes simulating economic, social and environmental
conditions at the country level, Threshold 21<http://www.threshold21.com/>
could be interesting.
Jim Thompson
Medical Cost Analysis & Forecasting
CIGNA Information Management
900 Cottage Grove Road A136
Hartford, CT 06152
Phone: 860.226.8607
email: jim.thompson@cigna.com

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"Jim Hines"
Senior Member
Posts: 88
Joined: Fri Mar 29, 2002 3:39 am

SD Country model

Post by "Jim Hines" »

Martin Busse asks about the National Model -- its current status and who
has worked on it.

Jay Forrester is continuing work on the model. Many people have worked
on the model including Bob Eberlein (this lists moderator), Alan
Graham, Gil Lowe, John Morecroft, Nat Mass, Nathan Forrester, Peter
Senge, John Sterman, me and others (maybe Christian Kampmann and Rogelio
Oliva).

I think everyone whos worked on the National Model would suggest to
anyone undertaking a similar effort to focus on one or more patterns of
behavior, rather than trying to model the system. Nathan Forrester told
me long ago that the National Model did not start out with a behavior
focus, but would have benefitted enormously if it had. Today, the
National model is very clearly focused on behavior patterns. The
patterns are: the economic long wave (a controversial oscillatory mode
with a fifty-year period), the business cycle (a 2-4 year oscillatory
mode), inflation, and real economic growth.

Question to Martin: Are you guys focused on a pattern of behavior and
which one? If youre not, what problem are you focusing on?

In addition to the National model, a number of others have done
country-level modeling work. Gerry Barney (I hope) subscribes to the
list and will describe the interesting work done the Millenium Institute
has done in this area. Khalid Saeed also subscribes to this list and
(if were lucky) will talk about some of the work hes been involved in.


There are a number of doctoral dissertations on various sectors or other
aspects of the National Model or modeling an economy. Among
dissertations you might be interested in the ones by Nathan Forrester
(macro economics from an SD perspective plus math techniques for
analyzing models), Bob Eberlein (model simplification), me (financial
sector), John Sterman (economic model with a focus on energy), Nat Mass
(he has book on business cycles), Peter Senge (government sector), and
Gil Lowe (financial sector). Alan Graham, who was second in command to
Jay during my tenure on the model, probably has a more complete list in
his head -- maybe hell respond, too.

Jim Hines
jhines@mit.edu
"Jim Hines"
Senior Member
Posts: 88
Joined: Fri Mar 29, 2002 3:39 am

SD Country model

Post by "Jim Hines" »

Martin,

Its good that you are using the "standard method" for each of your
sectors. But, Im concerned for you about developing the model by
sectors.

Dividing a model into sectors is a common strategy in SD, but not one
that always (usually?) works. The problem is that when the modeler
hooks the sectors together, he will be completing tens, hundreds,
thousands, even tens of thousands of loops (depending on the size and
"density" of the model). This means that the modeler can be confronted
with new, puzzling patterns of behavior at precisely the time the model
is most difficult to analyze (i.e. when its as big as its going to get).
The danger is multiplied when different people have developed the
different sectors (which is usually the whole idea behind dividing it
into sectors in the first place).

The MIT National model suffered from this approach, I think: A number
of dissertations (most of which I listed in the prior email) were done
as new sectors, developed separately from the larger model. The sectors
themselves were fine pieces of work, but incorporating them into the
larger model was difficult, as has been understanding the dynamics of
the National Model, though this is not only due to the early sectoral
approach -- the National Model really is a complicated model.

People sometimes mistakenly think the sectoral approach will work
because the approach is lauded in other fields. For example, the
sectoral approach is used by software developers. But in such fields
the approach works only because interactions between sectors can be
minimized (by good developers). Unfortunately in system dynamics, we
dont want to minimize those interactions -- the interactions are what
were interested in (otherwise why put the sectors together at all?).
So, what works in software development and maybe other fields wont
necessarily work in SD model development.

A better approach, I think, is to apply the "standard method" to the
real subject of interest -- The economy -- rather than to the
individual sectors.

The 5000 dollar question remains: How do you make use of a more than one
person in creating a model, if you DONT rely on a sectoral approach. I
know of one SD consulting firm that (at one time) could put three people
on a model -- but in this case only one of the people did the modeling.
One of the other two people would take charge of the data and the other
person would take the role of project manager (plus relationship manager
and coach).

Id be very interested in hearing on this list experiences or
speculations on how more than one person can participate in modeling.
(Note: Im mostly interested in approaches that dont rely on sectors,
but defenders of sectors are welcome to get their licks in (as if I
could stop you!)).

Jim Hines
jhines@mit.edu
Tom Fiddaman
Senior Member
Posts: 55
Joined: Fri Mar 29, 2002 3:39 am

SD Country model

Post by Tom Fiddaman »

>>There are a number of doctoral dissertations on various sectors or other
>>aspects of the National Model or modeling an economy. Among
>>dissertations you might be interested in ... Peter Senge (government
>>sector),

Peter Senge did the investment function. Barry Richmond worked on
government, though Im not sure if its an actual component of the national
model.

Many MIT theses are online at:
http://theses.mit.edu/

Older theses, not yet scanned, can at least be looked up for ordering:
http://libraries.mit.edu/services/barton.html

Tom
From: Tom Fiddaman <tom@vensim.com>
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