Tips From Our Members

Find Your Way in SD

This is a very handy guide that outlines how to navigate the Society website and introduces some of the available resources. Quickly find out how to find resources for your research, meet collaborators, and stay connected. There are also links to where to learn System Dynamics, including some free courses.

Molecules of Structure

Molecules of Structure is a handy reference for any modeler. Each section of this handbook covers a special behavior of a system with a specific rate structure. Many people have contributed to identifying and collecting the molecules over time. Professor Jim Hines gathered, expanded and represented the best examples of these building blocks for System Dynamics. Please download this marvelous effort and see how it will improve your modeling skills. Molecules of Structure now available in a Powersim Studio version. Please download them here.

MetaSD Model Library

This library gathered by Dr. Thomas Fiddaman contains replications of many classic models from System Dynamics and related fields. Citations are provided. Online resources for most of the articles may not be available, but links are provided where possible.

Many of the models in this library were recreated from published works by students in the MIT Sloan School’s PhD Seminar in System Dynamics. Thanks to several MIT students for the arduous process of reconstructing these models from published sources. Be forewarned that, since most of these models are replications, it’s possible that they contain errors introduced in the publication or reconstruction process.

Generally, the models in this library may be freely used and distributed, subject to authors’ copyright, which should be noted in the model file. Naturally you should acknowledge the hard work of the authors and implementers who created these files.

Introduction to System Dynamics

This online book was written by Professor Michael J. Radzicki and Professor Robert A. Taylor to introduce the concepts and “language” that make a systems-based study of such complex problems possible. Their intent is to provide the reader with a broad overview of the field of System Dynamics, acquaint him or her with the fundamental stock-flow-feedback structures that determine the dynamic behavior in systems, and motivate the reader to begin analyzing problems dynamically and holistically. Knowing how to speak and think in terms of systems and interconnections is a critical step in effective policy design, policy implementation, and consensus building.

System Dynamics Lab at Virginia Tech Tutorials

System Dynamics Lab is a web page in which you can find several documents and videos introducing basic and advanced topics in System Dynamics. These tutorials and resources have been gathered by faculty members in the department of Industrial and Systems Engineering at Virginia Tech. You can also find other resources from other place here.

Three Notes on Teaching Modeling (First Note, Second Note, Third Note)

These three Notes, written by Professor George P. Richardson and published in the System Dynamics Review in 2014 and 2015, describe a sequence of stages in learning the arts and craft of System Dynamics modeling. They were intended to provide a helpful, customizable framework for teachers designing their own System Dynamics courses but may be useful for self study. The framework describes a particular sequence of stages of learning and the exercises that would suit those stages: 1) Exploring existing models 2) Copying models 3) Adding structure 4) Correcting or improving structure 5) Modeling a “canned” model description 6) Modeling problems with vivid, well-known structure and dynamics 7) Modeling personally chosen problems.

*Access to the Models Mentioned in the Notes requires use of Vensim models. Instructions for accessing them are found in supplementary material on the Wiley web site, accessible by members of the Society.

Best Practices of System Dynamics Model Design and Construction with Powersim Studio

This guide addresses software quality in the construction of Powersim® Studio 8 System Dynamics simulation models. It is the result of almost ten years of experience with the Powersim suite of System Dynamics modeling tools (Constructor and earlier Studio versions). It is a guide that proposes a common look and feel for the construction of Powersim Studio System Dynamics models. This remarkable reference has been written by Professor Leonard A. Malczynski at Sandia National Laboratories.

The Validation of Commercial System Dynamics Models

This paper discusses the need for formal criteria for the establishment of confidence in, or the “validation” of, System Dynamics models constructed for fee-paying clients as opposed to for academic research purposes. The meaning of “validation” is first considered and the substantial differences between the consultancy and academic cases are discussed. That leads to a review of the System Dynamics literature on tests of validity. Finally, there is a discussion of the process of consultancy in System Dynamics. An outline of a set of formal tests is described.

Please find this paper authored by Geoff Coyle and David Exelby here.

Agile SD: Fast, Effective, Reliable

“When faced with a new problem, I start by identifying the stocks and how they are changing. I do not try to develop causal loop diagrams, though I know this is popular.” Forrester, 2013

Recent concern about the progress and impact of System Dynamics call into question the means by which the methods is deployed. Books, courses and published cases suggest we start by defining how the issue of concern is changing over time, then build qualitative casual-loop diagrams with stakeholders. The resulting shared mental model is taken to both encompass the scope of the issue and represent well the casual mechanisms involved. Stock-and-flow structures are then added to the model and data is sought with which to populate and formulate those structures, so as to create a working mathematical model. The process is difficult, time-consuming and unreliable; risking serious flaws and omissions, and producing different model for similar cases. The science of the method suggest a simpler process, which moves directly from the performance behavior to a qualified mapping of how stocks and flows are changing. From there, inter-dependencies are traced – again with quantified support – and significant feedback mechanism identified. Experience to data suggest that models are easier and faster to build, perhaps cutting the time and effort involved by as much as an order of magnitude, and the method builds in quality from start. Valuable insights also emerge throughout the process – reminiscent of the “agile” approach which now dominates the field of software development. Early experience suggests the approach may merit more widespread testing to confirm these benefits. The method is also consistent with a complementary approach, common among leading practitioners, of leveraging proven structures repeatedly across similar cases.

Please follow this link to read the whole paper by Professor Kim Warren.

Making Bass Diffusion Model in AnyLogic

AnyLogic supports different modeling techniques. This document covers System Dynamics modeling approach. There are many spheres where System Dynamics simulation can be successfully applied. AnyLogic allows you to create complex dynamic models using standard SD graphical notation. This tutorial will briefly take you through the process of constructing a simulation model using AnyLogic. It is intended to introduce you to AnyLogic interface and many of its main features. We will create a simple illustrative example—the product life cycle model, used for forecasting sales of new products.

The first 10 steps will take you through the process of construction of the classic Bass diffusion model. The model describes a product diffusion process. Potential adopters of a product are influenced into buying the product by advertising and by word of mouth from adopters – those who have already purchased the new product. Adoption of a new product driven by word of mouth is likewise an epidemic. Potential adopters come into contact with adopters through social interactions. A fraction of these contacts results in the purchase of the new product. The advertising causes a constant fraction of the potential adopter population to adopt each time period.

System Dynamics or Agent-Based models?

“Many novice modelers sense a need to choose between System Dynamics and agent-based approaches in their modeling projects. This is a false choice rooted in a confusion about what System Dynamics is.” With this statement, Professor Hazhir Rahmandad, Associate Professor of System Dynamics at MIT, begins his note on “System Dynamics or Agent-Based models? Wrong question! Seek the right level of aggregation.” Please read about the considerations modelers should seek for setting the appropriate level of aggregation.