7. A method as claimed in claim 6 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, that noisy version being specified using the level noise variable node in the layer of its parent variable node.
6. A method as claimed in claim 2 wherein creating and storing the graphical data structure comprises forming and storing a level noise variable node at each layer of variable nodes.