(1) A decision that negligence caused particular harm comprises the following elements:
(a) that the negligence was a necessary condition of the happening of the harm (‘factual causation');
(b) that it is appropriate for the scope of the negligent person's liability to extend to the harm so caused (the scope of liability ).
(2) However, if a person (the plaintiff ) has been negligently exposed to a similar risk of harm by a number of different people (the defendants ) and it is not possible to assign responsibility for causing the harm to 1 or more of them—
(a) the court may continue to apply the established common law principle under which responsibility may be assigned to the defendants for causing the harm; but
(b) the court must consider the position of each defendant individually and state the reasons for bringing the defendant within the scope of liability.
(3) In deciding the scope of liability, the court must consider (among other relevant things) whether or not, and why, responsibility for the harm should be imposed on the negligent party.