What is the burden of establishing causation in a medical malpractice case?

Once the plaintiff establishes causation, the burden shifts to the defendant to prove that the plaintiff failed to mitigate some of her loss or injury. If a plaintiff has not pursued a recommended course of medical treatment, the defendant must prove that the plaintiff acted unreasonably in declining the medical treatment and must prove the extent, if any, by which the plaintiff’s damages would have been reduced had she pursued that treatment: Chiu v. Chiu, 2002 BCCA 618 at para. 57.