3.1.2 Causation Lecture
A defendant’s conduct must cause the damage that the claimant has suffered.
Tort law uses a ‘but for’ test in order to establish a factual link between the conduct of the defendant and the injuries of the claimant. In other words, the question asked is ‘but for the defendant’s actions, would the harm have occurred?’ If the answer to this question is yes, then causation cannot be shown, and vice versa.
A relatively modern description of the test can be seen in Cork v Kirby MacLean Ltd  2 All ER 402, where the it was held that “if the damage would not have happened but for a particular fault, then that fault is the cause of the damage; if it would have happened just the same, fault or no fault, the fault is not the cause of the damage.”
In, Barnett v Chelsea and Kensington Management Committee  AC 613, the courts found that because injury to the claimant would have occurred regardless of the defendant’s conduct, there was no factual causation.
The All or Nothing Approach and the Burden of Proof
Matters of causation are decided on the balance of probabilities (i.e. 51%). Since the burden of proof rests with the claimant, the onus is on him or her to argue that had the defendant not acted negligently, their harm would likely not have occurred. Thus, if a court finds that there is a 55% chance that a defendant caused a claimant’s harm, they will hold the defendant entirely responsible for the harm.
This approach can be considered problematic because the courts are essentially treating the defendants as if they were 100% the cause of the claimant’s injuries, whilst in fact it is entirely possible that those injuries would have occurred regardless. The all or nothing approach can be seen as particularly problematic when dealing with ‘lost chance’ cases - these are described in detail in a later section of this chapter.
Specific Rules of Factual Causation
There will often be scenarios in which there are multiple causes of the claimant’s harm. In such scenarios, you should first work out if you’re dealing with concurrent causes (causes which happen at the same time) or successive causes (causes which take place one after the other). Each of these situations have their own rules which apply, as follows.
Multiple Concurrent Causes - The General Rule
Where there exists more than one possible cause of an injury or harm, the claimant does not have to show that the defendant’s actions were the sole cause of the injury suffered. Instead, it must simply be shown that the defendant’s actions materially contributed to the harm (Bonnington Castings Ltd v Wardlaw  for two concurrent causes; Wilsher v Essex Area Health Authority  AC 1074 for five different possible causes). According to the case law, whilst a 50% contribution is enough to bring a successful case, a 20% contribution is not.
Multiple Concurrent Causation - Exposure to Risk
Finally, there exists a line of cases where claimants have been unable to show that their harm has occurred as a result of the defendant’s conduct, but have been able to show that their employer has contributed materially to the risk of an injury occurring. In McGhee v National Coal Board  1 WLR 1, the claim was successful where the defendants had materially increased the risk of the claimant developing dermatitis.
This principle has become important where cases involve multiple illegitimate exposures to a risk. Its application can be seen in Fairchild v Glenhaven Funeral Services  UKHL 22 where the claimants were unable to demonstrate which of their multiple employers had actually caused the damage, just that one of them had. On balance of probabilities, it was improbable that each individual employer had caused it. The courts applied McGhee to deal with this problem, ruling that as long as each of the claimants could show that an employer had materially increased their risk of contracting mesothelioma (by illegitimately exposing them to asbestos), then they were entitled to claim full damages from that employer.
This did not mean that each employee could claim three times - they were only entitled to claim once for their injury. Whilst this might appear to punish the singled-out employer more than the others, that employer still had the option of suing the others for their contribution to the exposure, meaning that the cost of compensation could effectively be spread amongst the employers.
The same principle applies in cases even where the claimant has exposed themselves to asbestos voluntarily, as a matter of self-employment. In Barker v Saint Gobain Pipelines Plc  EWCA Civ 545, the claimant was exposed to asbestos for nearly 9 years whilst under the employment of the defendant. For the rest of his 30-year career, the claimant was self-employed, working with asbestos on three different occasions. It was held that Fairchild still applied, and that the defendant was liable for the claimant’s mesothelioma because of the material contribution by the defendant to the claimant’s illness. A 20% reduction in the claim’s value was made due to the claimant’s own contribution to exposure.
This type of liability can lead to individual employers being singled out for the activities of their peers. In Barker v Corus UK  UKHL 20, some of the potential defendants had since gone insolvent. The decision before the court regarding the defendant employer, therefore, was that, contrary to Fairchild, that each employer was only liable for a percentage of damages in proportion to their contribution to the claimant’s risk. In effect, this meant that the idea of joint and several liability applied in Fairchild was overturned, and instead it was held that the idea of ‘proportionate liability’ applied. This also meant that the share of damages attributed to insolvent defendants was not payable.
There was significant backlash from various groups representing mesothelioma victims, and s.3 of the Compensation Act 2006 has reversed the Barker v Corusposition - but only in relation to mesothelioma.
Multiple Successive Causes
There also exists a small band of cases involving multiple, successive causes of damage - that is, the claimant is harmed by two sources of damage, one after the other. The primary example here is Performance Cars Ltd v Abraham  1 QB 33, where the courts ruled that a claimant could not be compensated for the same loss twice. It was ruled that in such situations, the former, earlier defendant is liable.
Lost Chance Cases
There is also a category of cases which deal with the idea of losing a chance - for example, a claimant might have a disease with a 40% recovery prognosis if it is caught early enough. However, due to negligent misdiagnosis the disease might go unchecked, and become terminal in nature. This claimant would therefore want compensation for losing their 40% chance at recovery. Such situations are referred to as ‘lost chance cases’.
As a general rule, the courts are unlikely to compensate a claimant for the loss of a chance, where the lost chance is less than 50%. In Hotson v East Berkshire Area Health Authority  AC 750 the claimant was deprived of a 25% chance of not developing a hip deformity. Whilst the Court of Appeal awarded the claimant 25% of total damages on this basis, this reasoning was rejected by the House of Lords; since there was only a 25% chance that the hospital defendant had caused the injury, this did not satisfy the balance of probabilities.
In Gregg v Scott  2 WLR 268, the rule was applied regarding chance of survival. A doctor misdiagnosed the claimant’s lump as benign, when it actual fact it was cancerous. This caused a nine-month delay in the claimant’s treatment, and reduced his chance of survival from 42% down to 25%. Again, the Hotson rule meant that this was not actionable because it was more likely than not that the claimant would have died regardless.
It can therefore be seen that the law regarding lost chances is not without criticism. The problem with the status quo can be seen when the margins are made smaller; consider a situation in which Hotson had a 49% chance of recovering had the hospital properly diagnosed him. He would still be unable to claim, despite the hospital effectively changing his prognosis from a coin flip to certain deformity.
However, there is some merit to the Hotson position for claimants. For example: consider if a defendant had a 51% of getting better, but lost this chance due to medical malpractice. Under the Hotson principle, that claimant would be entitled to the full extent of damages, because on balance, they would have got better had malpractice not occurred. If, however, damages were calculated based on the lost chance itself, then this particular claimant would only be entitled to 51% of the total compensation for their harm, since there was a 49% chance the harm would have occurred regardless of malpractice.
Furthermore, the decision in Hotson makes it a lot simpler for the courts to work out the proper amount of compensation to be paid. If the decision of the Court of Appeal in Hotson were to stand, courts would have to spend significant time and resources working out the probability of certain things happening, down to the single percentage point. In contrast, the current situation means that there is no material difference between losing a 75% percent chance of recovery and losing a 70% chance of recovery - in either situation the claimant would be entitled to full damages for their condition.
Vindication of Rights Cases
Although lost chance cases demonstrate the problem with adhering strictly to the all-or-nothing approach to causation, there does exist a slim category of cases in which the courts have been willing to ignore the general rule due to policy considerations. Whilst examples are sparse, in Chester v Ashfar  3 WLR 927, the defendant doctor failed to warn the claimant that there was a 1-2% risk of her becoming permanently disabled as a result of an operation. She underwent the operation, and despite the operation being carried out correctly, the disabling complication occurred anyway. The claimant could not show that she would have avoided the operation had she known of the risk, but was able to argue that she would have delayed the operation by some time.
In applying the conventional but-for test, the courts found that they could not help the claimant - she would have likely undergone the operation anyway, and so the doctor’s negligence could not be described as having caused the harm - the risk would still have been run, simply at a later date. Nevertheless, the courts acknowledged the fact that the doctor had done wrong - patients have a right to know what they are consenting to. They therefore found against the defendant, despite the decision appearing to run contrary to conventional causation.
Cite This Module
To export a reference to this article please select a referencing style below: