What is the test for inferring causation between a breach of duty and loss?

Further, the authorities caution that it is appropriate for the court to infer causation only in limited circumstances. In Haag v. Marshall (1989), 1989 CanLII 236 (BC CA), 39 B.C.L.R. (2d) 205 Lambert J.A. said at 213: Where a breach of duty has occurred, and damage is shown to have arisen within the area of risk which brought the duty into being, and where the breach of duty materially increased the risk that damage of that type would occur, and where it is impossible, in a practical sense, for either party to lead evidence which would establish either that the breach of duty caused the loss or that it did not, then it is permissible to infer, as a matter of legal, though not necessarily logical, inference, that the material increase in risk arising from the breach of duty constituted a material contributing cause of the loss and as such a foundation for a finding of liability. Lambert J.A. went on to find that the plaintiffs could have led evidence of causation on the facts of that case. He held that in such circumstances the “inference” principle was not applicable.