Ventana software support forum

Posted: **Fri Apr 04, 1997 2:56 pm**

I hear and understand Phil Odences point about stocks and flows vs CLDs
and the last thing I want to do is to get into an extension of what
appears to be an endless argument between the protagonists.

However, my experience after several years of trying to find a way, any
way of getting working executives interested in the idea that it is
useful to look at issues as being systemic is that it is *much* easier to
get them started with very rough concept sketches and then move to CLDs
than to try to get them to understand stocks and flows. Even if they do
begin to understand them, they want (probably wisely) to leave the
plumbing to the experts, whereas some of them become quite enthusiastic
about using CLD and its variants as part of their strategic
conversations.

So I guess its a case of horses for courses - if the aim is to produce a
modeller, start them the right way with stocks and flows; if you want to
get an executive to be comfortable switching between Newtonian
andsystemic thinking,CLD type sketches may be more accessible.

Bill Godfrey
Bill Godfrey & Associates Pty Ltd
8 Reibey Place, Curtin, ACT 2605, Australia
Tel: (61) 6 282 2256
Fax: (61) 6 282 2447
email: bgodfrey@ozemail.com.au
BookWatch site: http://webtrax.com.au/BB/BookWatch.bbd

Posted: **Sat Apr 05, 1997 3:07 pm**

DEAR BILL, YOU MIGHT BE INTERESTED IN OUR TWO NEW BOOKS ON DYNAMIC MODELING
IN STELLA (MODELS ARE CONVERTABLE TO POWERSIM) AT THE FOLLOWING SITE:
http://www.springer-ny.com/biology/modd ... sforth.htm
ONE ON ECONOMICS INCLUDING GAME THEORY, ONE ON MODELING IN BIOLOGICAL
SYSTEMS, ONE ON MODELING IN A VARIETY OF DISCIPLINES.

Bruce Hannon, Jubilee Professor
Liberal Arts and Sciences
Geog/NCSA
220 Davenport Hall, MC 150
University of Illinois
Urbana, IL 61801
reply to: b-hannon@uiuc.edu
http://www.gis.uiuc.edu
217 333-0348 office
217 244 1785 fax

Posted: **Mon Apr 07, 1997 8:59 pm**

Barry Richmond viewed CLD vs stock-flow debate as a set of 3 skills in
progression, essential to what he calls systems thinking: 1.
system-as-cause thinking (ala GPRs "endogenous viewpoint"); 2. closed-loop
thinking (this is where CLD come in); 3. operational thinking (this is
where stocks and flow come in). He says (SDR vol 10, # 2-3, pp.140) that 1
and 2 are poor substitutes for 3, the essence of SD. He then argues through
examples why 3 is even more important than 1 and 2 to give systemic
insights that lead to changing mental maps. Jay Forrester in the same issue
on page 245 describes SD steps as 1. describe system; 2. convert
description to level and rate equations... and so on. No talk of CLD
until levels and flow rates have been identified ("CLs do not provide the
discipline to thinking imposed by level and rate diagrams in SD..." pp.
252). Please see above references for a longer description. This issue of
SDR is an *excellent* one, worth keeping and hauling whenever you move.

PS: For anyone still interested, transcript number for the program I
mentioned elsewhere is 1244 (in
http://www.uh.edu/campus/kuhf/engines/engines.htm)

Jaideep
jm62004@jetson.uh.edu

Posted: **Thu May 29, 1997 9:59 am**

Ill be teaching this 400 level business course this fall and was thinking of using SD as an
organizing framework for the course. Its a course in management science so the
perspective is that of optimal decision-making looking at production, market,
distribution and financing questions in the management of technology. So well also
be covering optimization techniques.

Its a new course for the University of Alberta and Ive not taught in the class for a few years.
Its also a new topic for me, so using SD would help me organize my thinking too.

Whats the best way to teach enough SD at the 400-level in the first few weeks
or parallel thoughout the course? Is Roadmaps the way to go?

Any ideas for building strong links between the SD framework and the optimization
subproblems?

The thoughts/advice of the group are appreciated.
............................................................................................................................

Iqbal Jamal
Office of Studies and Budget
City Manager Offices
City of Edmonton
1 Sir Winston Churchill Square
Edmonton, Alberta, Canada
T5J 2R7

(403) 496-8228
ijamal@gov.edmonton.ab.ca

Posted: **Fri May 30, 1997 1:22 pm**

Hi Iqbal,

I teach a Systems Management and Organization Theory class (graduate 500
level class) and I start with causal loops diagrams and then move to stocks
and flows diagramming.

Although initially at a loss why Senge omitted the "s" and the "o" (or the
"+" and the "-") from the Fifth Discipline, I now see the wisdom of his
decision. Although technically less precise, causal loops diagrams without
the "effect" indicator is much more accessible to students being exposed to
SD for the first time. I make the modeling more explicit when the stocks
and flows are introduced.

Once students are comfortable with stocks and flows, it should be an easy
transition to the optimization discussion. Perhaps a few models (Powersim,
iThink, etc.) that have some input parameters and which can run several
generations of a simulation would be good visual tools for the students.

Bill Braun
<medprac@hlthsys.com>
---------------------------
Medical Practice Systems Inc. (216) 382-7111 (Voice)
and The Health Systems Group http://www.hlthsys.com
Mergers - Planning - Management Services
Marketing - Managed Care - Education & Training

Posted: **Mon Jun 02, 1997 2:05 pm**

Regarding Causal Loop Diagrams...

We do not tend to use CLDs for model conceptualization, rather we
advocate that even novices go right to stocks and flows. (The wherefores
are longer discussion.) However, we do use CLDs as an after-the-fact
summary of feedbacks in a model, and for those we use a simple convention
that Barry Richmond invented.

Instead of using +/- or s/o, we use a little u-turn symbol (a U with an
arrowhead on one end) to indicate inverse relationships. Links without
symbols are by default sames.

The benefits are:
-1/2 as many direction symbols makes the picture less daunting;
-u-turn is a slightly more physical representation of the concept of an
inverse

***************************************************************************

Phil Odence
podence@hps-inc.com
High Performance Systems
45 Lyme Road, Suite 200
Hanover, NH 03755
voice- 603 643 9636 x107, fx- 603 643 9502, web- http://www.hps-inc.com

Posted: **Tue Jun 03, 1997 11:23 am**

Bill:

What do you model with the stocks and flow? Im tempted (a la Richmond) to use stocks
and flows first (I find that easier to explain) using SD first as an organizing paradym, then launch
into optimization "submodels" and use both approaches to solve business problems/cases.
Sound workable?

Have you used SD this to model the medical business? Im also looking at issues of technology
management, including health technologies/products.

Your comments/insights are appreciated.

Iqbal
ijamal@gov.edmonton.ab.ca

---------

Posted: **Tue Jun 03, 1997 1:34 pm**

Concerning Phil Odences statement that HPS advocates going straight to the
stock and flow representation:

Starting with S&F works fine when there is a prominent "main chain". Where
there are prominant feedback loops, starting with a CLD seems a more natural
first step.

I once asked Jay Forrester what he started with. He said that with Urban
Dynamics the stock and flow came first. With the Market Growth Model, loops
came first.

George Richardson and David Anderson (almost) always start with stock and
flows in their group modeling exercises. FWIW, I almost always start with a
causal loop diagram in group modeling exercises.

Regards,
Jim Hines
LeapTec and MIT
JimHines@Interserv.Com

Posted: **Wed Jun 04, 1997 12:33 pm**

Hello Iqbal,

The course I teach is not an SD course per se, so modeling is not the
centerpiece of course content. I use it more as a tool to introduce
managers to thinking differently. Becoming a competent modeler is not an
expected outcome for the students.

I am currently using PowerSim to develop several healthcare related models.
Both of these are being designed more along the lines of Flight
Simulators, accepting periodic managerial decisions and showing managers
the effect of their decisions over time.

One model looks at the interdependent relationship between clinical quality
and market share strategy. The other is more financially focused, taking
managers through a transition from fee-for-service to prepaid care, looking
at cash flows and capacity and the like.

On a related thread, I have historically started with causal loops but am
moving towards SD. I like the fact that stocks and flows are explicit and
find that the names given to objects are less of an issue when it is clear
that it is a stock, a flow, an auxiliary or a constant.

Going back to the classroom, generally I start with a macro model of the
system to establish the environment (or context), and then make the
subsystem model detailed. Since the primary purpose and output of the
modeling is a shift in managerial thinking, and students are expert at
reductionistic thinking, I like to force the expansionistic thinking first.

Bill
From: Bill Braun <medprac@hlthsys.com>

---------------------------
Medical Practice Systems Inc. (216) 382-7111 (Voice)
and The Health Systems Group http://www.hlthsys.com
Mergers - Planning - Management Services
Marketing - Managed Care - Education & Training

Posted: **Tue Jun 10, 1997 7:03 am**

>So I guess its a case of horses for courses - if the aim is to produce a
>modeller, start them the right way with stocks and flows; if you want to
>get an executive to be comfortable switching between Newtonian
>andsystemic thinking,CLD type sketches may be more accessible.

...they may be, but Ive seen exectutives readily grasp stock/flow
diagrams. Many people find them easier to read than CLDs. If exectutives
are working with modelers, they will have an easier time relating to the
model if they are working with the language with which it will be
developed. And, even in the event that theres no plan to do computer
simulation, dont discount the additional value of recognizing the stocks
and flows along with the feedback.

***************************************************************************
From: Phil Odence <podence@hps-inc.com>
Phil Odence
High Performance Systems
45 Lyme Road, Suite 200
Hanover, NH 03755-1221
voice- 603 643 9636 x107, fx- 603 643 9502, web- http://www.hps-inc.com

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