2. A method as claimed in claim 1 wherein creating and storing the graphical data structure comprises creating and storing a tree-based graphical data structure comprising layers of parent and child variable nodes.
2. A method as claimed in claim 1 wherein creating and storing the graphical data structure comprises creating and storing a tree-based graphical data structure comprising layers of parent and child variable nodes. 3. A method as claimed in claim 2 wherein arranging the training engine to update the statistics comprises enabling a child variable node to inherit a noisy version of the latent event score of its parent variable node.