Identifying Causal Relationships in DAGs: Example of D-A-Y

(a) The paths in the DAG D-A-Y are:

1. D -> A -> Y
2. D -> Y

(b) The causal relationship of D on Y is identified if we can find a set of variables that blocks all backdoor paths from D to Y. In this case, the only backdoor path is D -> A -> Y. To block this path, we need to control for A. So, the condition under which the causal relationship of D on Y is identified is if we condition on A.