This document is an attempt to help the reader begin to
understand what system dynamics is.
The document presents several responses to a challenge posed on
the system dynamics internet mailing list in 1997 by a Mr. Fabian Szulanski. Mr. Szulanski’s challenge to the list went
something like this,
I challenge you to define System Dynamics as if someone in an elevator were to ask you what it is, therefore leaving you less than 30 seconds to explain.
This challenge provoked quite a response. Here are some of the responses that I think
quickly (due to the elevator prescription!) capture some of the diversity of
views on system dynamics.
From Dr. George Richardson,
“I'd say ‘System
dynamics is the use of computer simulation for policy analysis in complex
systems. It's big contribution is
helping people to build progressively richer understandings of some dynamic
problem, and anticipate weaknesses in policy initiatives that would develop
over time.
“If you still have
time (and an audience), I'd say ‘It gets a lot of its power from a 'feedback'
perspective -- the realization that tough dynamic problems arise in situations
with lots of pressures and perceptions that
interact to form loops
of circular causality, rather than simple one-way causal chains. Humans are really good at thinking up all
that interconnected complexity and really weak at inferring its implications without the support of
simulation models.’
“And you are now at
the lobby level, so you probably won't be able to give them a nice list of
references...”
George P. Richardson
Rockefeller College of Public Affairs and Policy
Phone: 518-442-3859
University at Albany - SUNY, Albany, NY 12222
Fax: 518-442-3398
From Dr. Jay Forrester, the founder of the field of System Dynamics,
“System dynamics deals
with how things change through time, which includes most of what most people
find important. It uses computer
simulation to take the knowledge we already have about details in the world
around us and to show why our social and physical systems behave the way they
do. System dynamics demonstrates
how most of our own decision-making policies are the cause of the problems that
we usually blame on others, and how to identify policies we can follow to
improve our situation.”
[this may work if the
building is tall enough, and if the person really wanted to know]
Jay W. Forrester
Professor of Management, Emeritus and Senior Lecturer,
Sloan School, Massachusetts Institute of Technology
Cambridge, MA 02139
tel: 617-253-1571 fax: 617-258-9405
email: jforestr@mit.edu
From Dr. Eric Wolstenholme,
“It occurs to me that
one neat way of expressing an elevator (lift) definition of system dynamics
might be to present it as a mission statement. Here goes:
“The what, why and how
of system dynamics:
“What: A rigorous way to help thinking,
visualizing, sharing, and communication of the future evolution of complex
organizations and issues over time,
“Why: for the purpose of solving problems and
creating more robust designs, which minimizes the likelihood of unpleasant
surprises and unintended consequences,
“How: by creating
operational maps and simulation models which externalize mental models and
capture the interrelationships of physical and behavioral processes,
organizational boundaries, policies, information feedback and time delays; and
by using these architectures to test the holistic outcomes of alternative plans
and ideas,
“Within: a framework
which respects and fosters the needs and values of awareness, openness, responsibility and equality of individuals
and teams.”
Dr. Eric Wolstenholme (Eric@Cognitus.co.uk)
London Business School
From Dr. Barry Richmond,
"SD in a 30 second
elevator ride:
“To make sense of reality,
we all simplify it. Let's call these
simplifications "mental models."
We "simulate" our mental models in order to determine which
course of action to implement, which alternative to choose, which strategies
will best achieve our objectives.
“History shows that
our choices and decisions often leave us with holes in our feet. We so often
injure our feet two reasons: (1) the assumptions constituting the mental models
we build are not sufficiently congruent with the reality they are seeking to
represent, and (2) our simulations of these models do not correctly trace out
the dynamic consequences implied by the assumptions in the models.
“System Dynamics is an
approach which can help us to construct mental models which are more likely to
be congruent with reality and to then simulate these models more
accurately. System Dynamics thus
increases the likelihood that we will produce the consequences we intend.”
Dr. Barry Richmond
High Performance Systems, Inc.
From Dr. Ed Gallaher,
“I guess I would say
something like this:
"A 'system' means a grouping of parts
that operate together for a common purpose."
"As one example we could consider the
salmon ecosystem which includes fish, predators, commercial and sports
fishermen, the physical environment (cold, clear, running water with gravel
beds vs. clear cutting, grazing, silt, and warm water), dams, turbines, and
fish ladders." (I'd try to create
as broad a laundry list as possible, perhaps drawing my listener in to provide
suggestions as well.)
"Another very different
example might be the criminal justice system, which includes jails, policemen,
judges, criminals, probation officers, victims, families, and the perceptions
of the general public."
"I need to give
you several examples here, because system dynamics is not a
"sociology" tool, or an "ecology" tool, or a
"financial" tool. It is a
more general tool that let's us think about, and study, systems in
general."
"System Dynamics
provides us with two major tools. First
is a very simple, but powerful way to develop DIAGRAMS which specifically help
us talk to each other about the parts of a system and how they fit
together. As we build a diagram
together we are forced to talk about our underlying ideas and assumptions, so
they become much less fuzzy. We may
find that we -cannot- build a diagram that we both agree with. This is a HUGE step forward, because now we
have at least clarified our own understanding, and increased our understanding
of the other person's "mental model".
"After we have
developed a diagram, System Dynamics software allows us to put numbers on each
piece of the puzzle, or on each connection between two or more pieces of the
puzzle. Then we can run computer
simulations which describe the behavior of the "system" under
different conditions (more dams, fewer dams; more rain, less rain; more
logging, less logging).
“Is the model
‘right’? We don't know for sure. It can never be ‘perfect’.
“Does it help us
understand the system? Yes! Does it increase our awareness of other
factors that may be outside our usual viewpoint? Yes! Does it allow us to talk more intelligently to our
colleagues, our kids, and our
politicians? Yes! This approach will very often identify
"fixes that fail", despite the best intentions of idealistic policy
makers. And hopefully, it will lead us
fixes that don't fail . . . "
Ed Gallaher
Assoc. Prof. Pharmacology and Behavioral Neuroscience
Oregon Health Sciences University
Portland, OR
Ed Gallaher gallaher@teleport.com
From Dr. John Heinbokel
“I'm not sure about
the 30 second limitation, but one thing that has been useful for us at the
Waters Center is to split out "System Dynamics" into more manageable
pieces:
“1. ‘Systems thinking" which recognizes and
obliges you to conceptualize systems as interacting, potentially non-linear,
sets of feedback loops --some pushing, some pulling.
and
“2. ‘Dynamic modeling" which obliges you to
translate that mental model of the system into an explicit computer model that
is subject to challenge and clarification and the exploration of
"policy" options.
Dr. John Heinbokel
Oceanographer
Vermont Commons School
Burlington, VT
E-Mail: jhein@adelphia.net
From Bob Walker <rjwalker@sympatico.ca>
I have three elevator
speeches, never used verbatim, always paraphrased or modified to suit the
opportunity and the audience. I'm listing them here from their original sources
but with a few wording changes as I might be more inclined to actually use
them. None of these changes are intended to be corrections or amplifications,
just a matter of personal style. Please refer to the references for the
verbatims...
1. "System
Dynamics entails making three fundamental shifts of mind relative to our
traditional way of thinking. First, from linear, laundry list thinking to a
circular, closed-loop view of causality. This helps us move from a static
to a dynamic orientation and to much better understand how things change over
time. Second, a shift from an external to an internal focus on performance, how
we, not others, are responsible for most of the results we get. Third, a focus
on an operational view of how things actually work. This is in contrast to
traditional analysis methods based on statistical correlation of trends from
the past."
... from Barry
Richmond, An Introduction to Systems Thinking, iThink 4.0 documentation, High
Performance Systems Inc., Page I-12.
2. "We're
applying the mindset of control systems engineers to improve the dynamic
behavior of the systems we manage"
... from Geoff Coyle,
System Dynamics Modeling, Chapman & Hall, 1996, p.5. This is by far the shortest but only
effective for a limited audience, engineers of course, but finance types also
react well.
3. "System
Dynamics is a computer-aided approach to policy analysis and design. It applies
to dynamic problems, problems that change over time-arising in complex managerial
and economic systems - literally any dynamic systems characterized by
interdependence, mutual interaction, information feedback and circular
causality."
... from George Richardson, Modeling for Management I, Chapter 7, p. 47