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The five elementary structures of causality which all directed acyclic graphs are composed
Conventions for Effect Modification: We assume 
| ||
|---|---|---|
| Symbol | Meaning | Example |
 |
Boxed blue variable and blue path: observed effect-modification. Blue arrow need not have a causal interpretation |  |
 |
Dashed blue circle and blue path: effect-modifier not conditioned upon. Blue arrow need not have a causal interpretation |  |
