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Causal loops

A possibility to visualize complex interacting dynamics that may cause unexpected effects through feedbacks provides the so called causal loop diagram. To draw such a diagram starts out with identifying the causal influences on a phenomenon:

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Positive or negative signs can be used to indicate the kind of influence, that is, the direction of causality. Positive signs enhance, negative signs reduce an effect.

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Causal loop diagrams are effective means to analize a system's behavior. They can be used to get a first understanding of the consequences of positive (left graph below) or negative feedbacks (right graph below).

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The complexity of causal loops can be indicated in terms of the lengths of loops and in terms of the direction into which the dynamics in the loop reinforce themselves - their kind of feedback. Below two loops of length 2 - left with negative and right with positive feedback,

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Below a system of loop lengths 7 with three interacting loops, two with length 3 and one with length 4

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Different symbols for indicating the direction of the loops' feedback have been suggested. The avalanche symbol insinuates the (usually rather) escalating effect of positive feedbacks, whereas the balance symbol indicates the (usually rather) calming effect of negative feedbacks.  Most commonly used however, (and probably most simple to use) are the algebraic signs PLUS and MINUS:

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The overall dynamic of a loop with several sub-dynamics or sub-loops can be derived by counting the MINUSes in a loop. An even number of MINUSes indicates a positive feedback. An odd number of MINUSes indicates a negative feedback.

Once again: positive loops (or feedbacks) tend to have escalating effects, negative loops (or feedbacks) tend to have calming effects. It is important to keep this difference in mind (see also the related effects of stocks and flows)

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