Table 2.

Rules to establish whether a pathway in a causal diagram is open or blocked

Rule No.Type of PathNo. of Colliders on PathAim of AdjustmentHow to Establish if Path is Open or Blocked
1CausalN/ALeave open (for estimation of total causal effect)The path will be open providing that no variables along it are conditioned on (otherwise, it will be blocked)
2Noncausal0Block noncausal pathwayThe path will be blocked if at least one variable along it is conditioned on (otherwise, it will be open)
3aNoncausal1Block noncausal pathwayThe path will be open if the only variable conditioned on is the collidera (otherwise, it will be blocked)
3bNoncausal>1Block noncausal pathwayThe path will be open if all of the collider variablesa (and no noncollider variables) are conditioned on (otherwise, it will be blocked)
  • N/A, not applicable.

  • a Or descendant(s) of the collider(s).