What are causal loop diagrams?
How to draw causal loop diagrams
Diagram guidelines
Purpose
Causal loop diagrams are similar to both multiple cause and sign graph diagrams in purpose and structure. They have been developed out of the systems dynamics movement and are most used in organisational settings. Causal loop diagrams are used to graphically depict dynamic interrelationships among variables you may not have considered before. They allow you to see how parts of a system that are separated by location or time might nonetheless interact to generate problems. They can be used as the basis for a computer simulation model. The most common behaviours modelled this way are often presented as systems archetypes (e.g. fixes that fail, shifting the burden, limits to success, escalation, tragedy of the commons, etc.).
Elements
- A title.
- Phrases.
- Arrows linking the phrases with ‘s’ and ‘o’ signs on the arrows, indicating the direction of change.
- ‘B’ or ‘R’ denoting balancing or reinforcing feedback loops, respectively.
Conventions
- The words or phrases represent variables.
- The arrows represent links between the variables, with the assumption that when variable A changes, variable B changes.
- A relationship where a change in A leads to a change in B in the same direction is denoted by an ‘s’ while where a change in A leads to a change in B in the opposite direction is denoted by an ‘o’.
- A closed circle of variables and links makes a feedback loop. Where the signs are all ‘s’ or all ‘o’ then this is called a reinforcing (or positive) feedback loop, and where there are both an ‘s’ and an ‘o’ then it is a balancing (or negative) feedback loop.
- A delay in a relationship is sometimes marked by a double line break in the linking arrow.
- Thought bubbles can be added to reveal the mental model behind links and identify the places where human choices are made.
Guidelines
- Formulate the core problem and tell the story of the problem behaviour. Choose the key variables you want to work with and name them precisely. Use nouns or noun phrases rather than verbs (e.g. ‘orders shipped’ rather than ‘ship’). Be sure your variable fits into phrases, such as ‘level of’, ‘amount of’ or ‘size of’. Use a neutral or positive term whenever possible to avoid confusion that can arise with negative forms of nouns. Include intangible variables (e.g. morale) where appropriate as well as tangible variables (e.g. workers, buildings).
- Graph the variables’ behaviour over time and hypothesise about how the variables might be interrelated. Be careful to be as accurate as possible by acknowledging any distinctions between a proportional change in the same direction and a direct change in the same direction (or vice versa).
- Use links and arrows to show the direction of the variables ‘cause and effect’ relationships. Mark the links with an ‘s’ and an ‘o’ to show the nature of (same or opposite) the link. Label the centre of every loop with either an ‘R’ (for reinforcing) or a ‘B’ (for balancing).
- If a variable has multiple consequences, try lumping them into one term while finishing the rest of the loop. You can ‘unpack’ these later when you are ready to explore the significance of specific interventions.
- Almost every action has differing long term and short term consequences. To show increasingly longer term consequences or side effects add new loops or links to your diagram.
- If a link between two variables is not clear to other people and requires a lot of explaining, try redefining the variables or inserting an intermediate variable to clarify the connection.
- Check the reasoning behind your causal loop diagram by going around the loop and telling the story depicted by the links and the s and o labels.
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