Ventana software support forum

Posted: **Tue Apr 04, 2000 6:58 pm**

Dear All,
I am a spanish student of Cranfield University (UK)
and I am doing a Thesis about "Systems Thinking and the
supply chain". I would very grateful if you could give
information (books, articles, web sites...) about the
different methodologies to draw influence diagrams (arrows
with sign and level and rates). I would like also to
receive information about causal loop diagrams as many
people use them as influence diagram. I know Coyle and
Wolstenholme methodologies and I would like to study these
deeply and some others. I am also interested in knowing how
to validate a diagram without quantitative systems dynamics
(i.e. how to know that I have included all the variables
and that the relations between them are right without using
the computer).
Thank you in advance,
Nacho

ignacio de mora lopez
Cranfield University
I.De-mora-lopez.1999@Cranfield.ac.uk

Posted: **Sat Apr 08, 2000 8:25 am**

hi,
validating a system dynamics diagram without simulation has in our
experience never payed out unless in reinforcing (erroneous) preconceptions.
For this we think are responsible two reasons:
1. the role of levels comes out only in simulation
2. real world models are almost without exception highly nonlinear, so we
think only sober siulation work will reveal the models characteristics
including whatever one wants to validate

"validating a model" in current practice based only on a diagram is one of
the receipts sold by software such as micrographics flow-charter for static
structure analysis..

// yours sincerely ulrich la roche
fast focus consulting
heilighuesli 18, CH-8053 Zuerich,
switzerland
fax +411 382 1349
From: ularoch@ibm.net

Posted: **Mon Apr 17, 2000 12:22 pm**

Hello Ignacio --

Im a practicing consultant and corporate trainer, not academic.

Here are a couple of points that Ive found very useful in my
teaching and practice:

1) consider each causal relationship assuming all else is constant.
If all else constant how would a change in A affect B? Same
direction? or opposite?

2) most people have trouble making their variables precise. I coach
people that every variable on a causal loop diagram should be
something they can show on a graph vs. time. This eliminates a whole
host of problems (imprecise notions, unclear +/- sense, event vs.
variable).

>.I am also interested in knowing how
>to validate a diagram without quantitative systems dynamics

This is certainly not possible in any absolute sense.
The only validation you have is "face validity".. that is, does the
structure make sense.

-=- Rick Karash
--

Richard Karash ("Rick") | <http://world.std.com/~rkarash>
Speaker, Facilitator, Trainer | mailto:Richard@Karash.com
"Towards learning organizations" | Host for Learning-Org Discussion
(617)227-0106, fax (617)523-3839 | <http://www.learning-org.com>

Ventana software support forum

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