Professor Graham Law, who recently joined the university and CaHRU as Professor in Medical Statitics, delivered the latest of CaHRU/LIH’s Implementation Science and Research Methods seminar series – on Causal Models and the use of Directed Acyclic Graphs. Professor Law set out the epidemiological context for the seminar. Epidemiology is the study of disease. The scientific methods used within epidemiology aim to discover the determinants of disease. The state of having the disease is the outcome. Causal models seek to examine the factors that contribute to this outcome. Causation is not usually dealt with by statistics. Instead, statistics concerns itself more with associations and relationships between variables.
A Directed Acyclic Graph (DAG) comprises variables (nodes) and arrows between nodes (directed edges) such that the graph is acyclic, i.e., it not being possible to start at any node, follow the directed edges in the arrowhead direction, and end up back at the same node. In seeking to represent causation, DAGs typically display a series of factors, mediators and outcomes. Having explained this, Graham split the audience into two groups and challenged them to create their own DAGs to display all the possible factors involved in whether sunlight causes lymphoma. The interactive nature of the seminar engaged the audience. The fun nature of the concluding task made a potentially complicated subject easier for the audience to understand and apply.
By Viet-Hai Phung