What is the test for establishing a contributory factor in a motor vehicle accident?

[161] Causation in tort is established where the plaintiff proves on a balance of probabilities that the defendant caused or materially contributed to the harm. A contributing factor will be considered to be material if it falls outside the de minimis range: Athey v. Leonati, 1996 CanLII 183 (SCC), [1996] 3 S.C.R. 458, [Athey cited to the S.C.R.]. A negligent defendant will not be excused from liability merely because other causal factors were at play in producing the harm. So long as it is part of the cause of her injuries, the defendant will be fully liable to the plaintiff even if the negligence alone was not enough to create her injuries: Athey.