Causal Diagrams

Sander Greenland & Judea Pearl

From their inception in the early 20th century, causal systems models (more commonly known as structural-equations models) were accompanied by graphical representations or path diagrams that provided compact summaries of qualitative assumptions made by the models. Figure 1 provides a graph that would correspond to any system of five equations encoding these assumptions: 1. Independence of A and B 2. Direct dependence of C on A and B 3. Direct dependence of E on A and C 4. Direct dependence of F on C 5. Direct dependence of D on B, C, and E The interpretation of ‘direct dependence’ was kept rather informal and usually conveyed by causal intuition, for example, that the entire influence of A on F is ‘mediated’ by C . By the 1980s, it was recognized that these diagrams could be reinterpreted formally as probability models, which opened the visual power of graph theory for use ...

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