Scriptapedia/Chickens and Eggs

Context and Purpose of the ScriptEdit

This script is used to introduce concepts of causal loop diagram (CLD) and provide an example of feedback those without knowledge of system dynamics. The purpose of the script is to provide a universal and easy to understand metaphor for complex systems.



Primary Nature of Group TaskEdit



Preparation time: 5 minutes

Time required during session: 10 -15minutes

Follow-up time: 0 minutes


  • Markers or pens
  • A white board or flip chart papers


  1. A story of chickens reproduction, growth, overcrowding, and injuries.
  2. A graph over time of chicken population growth dynamic.
  3. A drawing with chicken crossing roads if preferred.  
Example of Chicken and Eggs


  1. A causal loop diagram of chicken population growth dynamic with variables, polarity, feedback loops, and delays.
  2. Familiarity with the concepts of feedback loops (reinforcing and balancing), causal relationships with polarities between variables, and how to interpret dynamics from a causal loop diagram.  


Modeler or facilitator with training in system dynamics or community based system dynamics


  1. First, the facilitator will tell a story of chickens reproducing, population growth, overcrowding, and injuries, while drawing a picture of the narrative.
  2. Then, the facilitator will present a graph over time to describe this dynamic – of chicken population growth with a hope of sustained growth, and a fear of collapse.
  3. The facilitator then draws a causal loop diagram to represent the reinforcing and balancing loops of the story.  The facilitator then explains that the model functions as a “dynamic hypothesis” of the structure that may create this behavior.
  4. The presentation should highlight
    • Polarity,
    • What a variable means (it varies)
    • Feedback loops (reinforcing and balancing)
    • Delays
  5. (S)he then asks if there are other factors or structures, and can add on other sources of injuries, other factors that reduce eggs, etc. and maps those factors onto the CLD, to demonstrate that models are meant to be tools for dialogue and thinking.  As participants nominate additional links, the facilitator adds those links to the model.

Evaluation CriteriaEdit

Participants contribute variables indicating understanding of dynamic variables


Originally developed by Brian Biroscek. Refined and expanded by Peter Hovmand, Ellis Ballard and the Social System Design Lab