Substantial-Factor Test
Definition
A test for causation that applies if (1) multiple forces combined simultaneously to cause a victim's harm, (2) any one of the forces would have been sufficient by itself to cause the harm, and (3) it is impossible to tell which force caused what portion of the harm. If an actor's negligence was a substantial factor in causing the harm, then that negligence will be treated as the actual cause of the injury, notwithstanding any other independent forces.