 The structural equations above can be represented in terms of a directed graph. The variables in the set V are represented as nodes in the graph. An arrow directed from one node X to another Y represents the fact that the variable X appears on the right-hand side of the structural equation for Y. In this case, X is said to be a parent of Y. Exogenous variables are represented by nodes that have no arrows directed towards them. A directed path from X to Y in a graph is a sequence of arrows that connect X with Y. The directed graph of the model described above of Billy and Suzy example is depicted in Figure 1 below: