What is the standard of proof in the context of workers’ compensation law?

With respect, this position stems from the confusion of two different legal concepts, namely the standard of proof and the test for causation. The standard of proof refers to the degree of certainty required to establish a fact, whereas the test for causation refers to the legal analysis used to make a factual determination, specifically a relationship of cause and effect. So while the legislation and policy tell us that the standard of proof is preponderance of the evidence, we must look elsewhere for guidance on the test for causation. In this regard, it is a long‑standing principle of both tort law and workers’ compensation law that the test for causation does not require a single or dominant cause. As long as the work-related cause materially contributed to the injury then it will be compensable: see Athey v. Leonati, 1996 CanLII 183 (SCC), [1996] 3 S.C.R. 458 at paragraph 17; Ison, supra at 58. Thus in cases like this one, the question is whether it is more likely than not (standard of proof) that the physical demands of the job played a role in triggering the aggravation (test for causation). [emphasis added and omitted]