Reflecting on the Afghanistan counterinsurgency diagram in the NYTimes, Scott Johnson asked me whether I found causal loop diagrams (CLDs) to be useful. Some system dynamics hardliners don’t like them, and others use them routinely.
Here’s a CLD:
And here’s it’s stock-flow sibling:
My bottom line is:
- CLDs are very useful, if developed and presented with a little care.
- It’s often clearer to use a hybrid diagram that includes stock-flow “main chains”. However, that also involves a higher burden of explanation of the visual language.
- You can get into a lot of trouble if you try to mentally simulate the dynamics of a complex CLD, because they’re so underspecified (but you might be better off than talking, or making lists).
- You’re more likely to know what you’re talking about if you go through the process of building a model.
- A big, messy picture of a whole problem space can be a nice complement to a focused, high quality model.