System Dynamics in the Elevator

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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... _________________________________________________________________

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] _________________________________________________________________

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. _________________________________________________________________

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 for 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. _________________________________________________________________

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. _________________________________________________________________

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:

Systems thinking which recognizes and obliges you to conceptualize systems as interacting, potentially non-linear, sets of feedback loops --some pushing, some pulling.
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.

_________________________________________________________________

From Bob Walker

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...

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.)
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.)
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)

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