What Is the Test for Causation in Personal Injury Matters and How Is Causation Determined?
Causation simply means that, in terms of a personal injury, someone else's negligence was a cause of your injury. There are two methods to prove causation.
When a Court considers causation, it considers two sub-issues first:
1. What test of causation governs the situation?
2. Based on the facts, can the plaintiff prove on the balance of probabilities that the defendant’s breach of the standard of care was a cause of their loss?
As outlined in the Supreme Court of Canada decision, Clements v. Clements, the standard test of causation in negligence is the ‘but-for’ test. That is ‘but for’ the collision, would the injuries have occurred. The ‘but-for test’ requires the application of three discrete steps:
1. Has the harm that is alleged to have been caused by the defendant been identified?
2. Does the defendant’s conduct satisfy the standard of care of the reasonable person, being sure to leave all other facts the same?
3. Would the plaintiff’s harm have occurred if the defendant had been acting with reasonable care?
Under these tests, the plaintiff need not prove that the defendant's negligence was the sole, immediate, direct or even the most important cause of his or her loss, but only that the defendant’s negligence was a cause on the balance of probabilities.
As stated in the Supreme Court of Canada decision, Snell v. Farrell, this means that the plaintiff is not required to prove causation to the standard of scientific certainty. If the plaintiff's injury would not have occurred but for the defendant’s negligent act, then that act is a cause of the injury and that is enough. However, if the plaintiff's injury would have occurred regardless of the defendant's negligent act, then that act will generally not be held to be a cause. Notably, a plaintiff may have two or more distinct injuries or more sets of injuries, each of which must be separately analyzed in terms of causation.
The trial judge will then take a robust and pragmatic approach to deciding if a plaintiff has established that the defendant’s negligence caused or contributed to their loss. The worsening of a prior injury will be thoroughly considered in the process. Was this injury made worse by the subject accident? Is there a new or worsening injury superimposed upon an old one?
The ‘Material Contribution to Risk’ Test
In certain circumstances, a court may also choose to apply ‘the material contribution to risk’ test. This test, however, is only used on a limited basis. The material contribution test removes the requirement of “but for” causation, instead substituting it for proof of ‘material contribution to risk’. This latter test is implemented where it is impossible to determine which of many negligent acts by multiple actors, in fact, caused the injury.
It must be established that one or more of these actors did, in fact, cause or contribute to the subject injuries. In this situation, because each negligent act points the finger at the other, this test is the only method available to arrive at the truth. In this way, it would be difficult, if not impossible, by any other test, for the plaintiff to show on a balance of probabilities that any one of the accidents, in fact, caused the injury.
In the final analysis, the two tests described earlier, are the only methods available to our judicial system to practically determine causation in the various kinds of accidents our Courts encounter. There is no doubt that the ‘but for’ test is most often used in single accident cases: in motor vehicle accident and occupier liability act cases. When applying the ‘but for’ test, the sequence of events often occurs within a split second: impact and injuries intertwined by its speed, its impact and the plaintiff’s vulnerability.
That said, causation is not an issue in Canada Pension Plan and Short and Long-term disability cases because the nature and extent of the injuries need only be proven, not the cause. The ‘material contribution to risk’ test is only used in limited circumstances. It can be applied to complicated, multiple liability situations.
For example, regarding liability, it is sometimes encountered in hunting cases where strict proof of causation is not available, especially where more than one hunter is involved. It can otherwise be applied where there is more than one accident and causation is difficult, if not impossible, to prove in using the ‘but for’ test. If this issue should arise for you, we would suggest that you consult the lawyers at Littlejohn Barristers to discuss your legal rights at (705) 725-7355.