Causal loop diagram

Systems & feedbackField guide · Systems & feedback · 3 of 6

Why do some changes snowball while others settle?

Over variables and effects, a causal loop diagram shows each effect’s polarity, the loops the effects close, delays, boundaries and external drivers.

Marks

• variable

• effect

• polarity

• delay

• loop

• reinforcing loop

• balancing loop

• boundary

• external driver

• gapdrawn as an ordinary variable

• nonlinear effect

• evidence coding

• leverage point

• behavior note

• viewpoint tag

How each mark is drawn and read: chapter 4, What the notation expresses.

A line with an arrowhead

A line with an arrowhead is an effect: a change in the variable at its tail causes a change in the variable at its head. Its polarity gives which way, + for the same direction and − for the opposite.

A week of short nights

Sleep debt raises afternoon caffeine, caffeine cuts hours slept, and fewer hours slept raise sleep debt: two − effects make the loop reinforcing (chapter 4’s week of short nights).

When to draw one

Draw one when a change seems to feed itself, when something drifts back however hard anyone pushes on it, or when a fix works for a while and then stops (chapter 4’s signals).

When not to draw one

When the answer turns on amounts, a stock & flow diagram carries the numbers. An order of steps is a numbered list, and a change that feeds nothing back is a sentence (chapter 4, what stays informal).

Reasoning and polish

• Reasoning5 of 5
• Polish4 of 5rough loop → presentation model

1. One loop, the polarity of each effect checked
2. Several interacting loops, delays, and loop names
3. Loop dominance, behavior notes and leverage points

Related types

• An influence map is converted to a causal loop diagram: its variables and causal claims carry over, and its influence claims, weights and clusters are left behind.
• A causal loop diagram is redrawn by hand as a stock & flow diagram, what accumulates becoming stocks, filled and drained by flows that signals set.
• A feedback control diagram is drawn as a causal loop diagram is, with a role written above each variable that plays one, its effects called signals.
• A system archetype is drawn with a causal loop diagram’s marks, with roles and a declared archetype written on it.

In this book

• Chapter 4, Loops That Amplify, Loops That Correct: variables, polarity, loops, the parity rule, the gap, delays, behavior notes and leverage points; exercises CL 01–05.
• Chapter 5, Delays, External Drivers, and Competing Loops: boundaries, external drivers, nonlinear effects, evidence coding, viewpoint tags and loop dominance; exercises CL 06–10.

Sources

• Donella H. Meadows, Thinking in Systems: A Primer (Chelsea Green, 2008), chapter 1, on reinforcing and balancing loops, and chapter 2, on delays and shifting dominance.
• Donella H. Meadows, Leverage Points: Places to Intervene in a System (Sustainability Institute, 1999), on leverage points.
• John D. Sterman, Business Dynamics: Systems Thinking and Modeling for a Complex World (Irwin/McGraw-Hill, 2000), chapter 5, on causal loop diagrams: polarity, a loop’s kind, delays, and naming variables as nouns rather than actions.
• John D. Sterman, “System Dynamics Modeling: Tools for Learning in a Complex World”, California Management Review 43, no. 4 (2001), a short introduction to the same ideas.
• George P. Richardson, “Problems with Causal-Loop Diagrams”, System Dynamics Review 2, no. 2 (1986), on what polarity does and doesn’t mean.