Graph Edge Types
Edge Types Present Relationships Absent Relationships
A --> B A is a cause of B.
It may be a direct or indirect cause that may include other measured variables. Also, there may be an unmeasured confounder of A and B. 		B is not a cause of A
A <-> B There is an unmeasured confounder (call it L) of A and B. There may be measured variables along the causal pathway from L to A or from L to B. A is not a cause of B.
B is not a cause of A.
A o-> B Either A is a cause of B (i.e, A --> B) or there is an unmeasured confounder of A and B (i.e, A <-> B) or both. B is not a cause of A.
A o-o B Exactly one of the following holds:
  1. A is a cause of B
  2. B is a cause of A
  3. there is an unmeasured confounder of A and B
  4. both a and c
  5. both b and c
If an edge is bold (thickened) that means there is no latent confounder. Otherwise, there is possibly latent confounder.
If an edge is green that means it is definitely direct. Otherwise, it is possibly direct.