Subject: Modeling: Archetypes vs. Stock & Flow

Posted by Gene Bellinger on 12/27/2009
In Reply To:Modeling: Archetypes vs. Stock & Flow Posted by Gene Bellinger on 12/24/2009

Message:

G’Day All

Some of the feedback I’ve received on the subject article, http://snipr.com/ttz0s, has provided an awareness that seemed worth sharing.

First, it seems that some consider “Systems Archetype” implies “Causal Loop Diagram” and nothing beyond that.

I have always considered a set of interactions that have a well defined structure and exhibit a characteristic pattern of behavior and frequently occur to be a Systems Archetype. And whether I describe this set of interactions and their implications in words, as a Causal Loop Diagram, as a Stock & Flow diagram, or as a Simulated Model, it’s still the same Systems Archetype. Admittedly the Causal Loop Diagram and the Stock & Flow Diagram are only qualitative views while the Simulated Model is a quantitative view. Each seems to have utility. It was because of this view on my part that I implemented each of the 16 archetypes I’m aware of as a Causal Loop Diagram, a Stock & Flow Diagram and a Simulation that can be run in a web browser. See: http://snipr.com/taeoj

Secondly, there seems to be a thought that: “Stock and flow diagrams without going through the process of calibration, sensitivity testing, validation and other steps are not useful.”

I have always considered there to be a deepening of awareness and understanding one can delve into too a level that suits their need in the context of the situation as follows.

• Systemic Ignorance – which is where most of the world operates most of the time, which is what it is by definition. Not a great place from which to operate.
• Causal Loops – while only qualitative investigating a situation with causal loops provides me with a somewhat better chance of a sound decision than Systemic Ignorance.
• Stock & Flow – while still only qualitative investigating a situation with a stock & flow diagram forces me to be more explicit regarding what flows and what accumulates and I find it is quite improvement over simply employing causal loops.
• Modeling & Simulation – employing stock & flow diagrams, calibration, sensitivity testing, and related steps provide a quantitative awareness which provides me the soundest perspective from which to make decisions.

And, the above causes me to recall an email from Erling Moxnes, when I asked under what conditions is a System Dynamics approach unwarranted. His response was, “There is also a need to consider the cost and timeframe. The investment should be commensurate with the potential benefit. There are times where all that is possible will be a causal loop diagram, or a stock and flow diagram; however these could be very useful.”

be well,
Gene

Follow Ups:

Modeling: Archetypes vs. Stock & Flow - Della Robinson 12/28/2009 
Modeling: Archetypes vs. Stock & Flow - Sharon Villines 12/28/2009 
Modeling: Archetypes vs. Stock & Flow - Bill Braun 12/28/2009 
Modeling: Archetypes vs. Stock & Flow - Della Robinson 12/27/2009 
Modeling: Archetypes vs. Stock & Flow - Tony Phuah 12/27/2009