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218 NEGLIGENCE: CAUSATION AND CONTRIBUTORY NECLICENCE

odd to ignore what we know has happened and take into account what might have happened.⁵⁶

Proof and causation

Causation is not a matter of historical fact in quite the same way as, for example, how fast the defendant was going or what was the claimant's income before the accident, for it involves an inquiry into what would have happened if the defendant had not committed the wrong. However, it is treated in the same way. The burden of proving that the harm would not have occurred if the tort had not been committed rests, as a generał rule, upon the claimant. If he succeeds in showing this on a balance of probabilities then the hypothetical non-occurrence of the harm is treated as being conclusively established even though there may be a substantial chance that it would have happened just the same, and the claimant recovers all the damages flowing from the wrong, not a proportion of them discounted by that chance."⁷ We must contrast with this the issue of what may happen in the futurę, or what would have happened in the futurę had it not been for the defendant's wrong, both of which have obvious relevance to the quantification of the claimant's damages. Here the balance of probabilities is irrelevant and "the court must make an estimate as to what are the chances that a particular thing will or would have happened and reflect those chances, whether they are morę or less than even, in the amount of damages which it awards".⁵⁸ In such cases, where proof "is necessarily unattainable, it would be unfair to treat as certain a prediction which has a 51 per cent probability of occurring, but to ignore altogether a prediction which has a 49 per cent probability of occurring".⁵⁹ The generał "vicissitudes of life" are usually simply allowed for in the generał discount on damages which also takes account of the fact that the claimant will be receiving a lump sum which will generate income⁶⁰ but if there is evidence that the claimant was in some way at greater risk of loss from some other cause (for example if he has a weak heart or is in insecure employment) the discount may be greater. Equally, the damages may in a suitable case be increased to allow for contin-gencies⁶¹—for example it has been commonplace in cases of head injury

^ Lord Wilberforce in lobling paid a good deal of attention to the fact that compensation is not merely a matter of tort damages and that the claimant's position with regard to other sources of money may determine whether he is under-or over-compensated. With respect however, this is the generał problem of offsets and deductions of collateral benefits (Chap. 22 below) and raises no morę issues in multiple causation cases than in those where the issue of causation is elear.

^S7 For an example sec Athey v. Leotuiti (1996) 140 D.L.R. (4th) 235 (road accident: claimant having history of back trouble; subsequently developed hemiated disc; trial judge's finding interpreted as meaning that the accident madę a 25% causal contribution to the herniation; claimant recovered in fuli; had the finding meant that there was a 25% chance that the accident madę a causal contribution to the herniation, claimant would have failed).

** Malleł v. McMonngle (19701 A.C. 166 at 176, per Lord Diplock.

* Malec v. I-C. Hutton Pty Ud (1990) 92 A L K 545 at >49.

See para. 22.25. below.

^ftł For an example of very difficult facts see Langford v. Hebran 120011 P.I.Q.R. Q13 (career prospects of kick boxer).

to award something for the risk that epilepsy may develop.^h2 If, however, the claimant fails to show on a balance of probabilities that the harm was caused by the defendant's tort he recovers nothing, even though there _may be a possibility that it was. In Wilsher v. Essex Aren Health Authoriiy* the claimant, born prematurely, succumbed to RLF, a retinal condition causing serious damage to his sight. A possible cause, or contributing cause, of this was an excess of oxygen caused by a mistaken placing of a catheter'’⁴ but the conflicting expert evidence at the trial identified a number of other possible causes which were not attributable to the fault ₀f the defendants and the failure of the trial judge to find that the mistake was morę likely as a cause than these others⁶* meant that there had to be a retrial on the causation issue.

6.10

An attempt to apply the same approach to causation as is applied to ąuantification was rejected by the House of Lords in Hotson v. Enst Berkshire Health Authority.⁶⁶ The defendants failed correctly to diagnose the claimant's condition after a fali and there developed a serious disabil-ity of the hip joint. On the facts there was a 75 per cent risk that this disability would have developed even if the claimant had been treated pnoperly⁶⁷ but the trial judge (and the Court of Appeal) held that he was entitled to damages representing 25 per cent of his fuli loss. This was reversed by the House of Lords: the judge's findings of fact amounted to a conclusion that on a balance of probabilities the disability would have occurred anyway and that the fali was therefore the sole cause of the loss. On this basis there was no foundation for awarding damages for loss of

** Though sińce the Administration of Justice Act 1982 such a case would probably be morę suitable for the award of provisiona! damages: para. 22.24, below.

^ 119881 A.C. 1074.

^M A further point on breach of duty is discussed in the Court of Appeal but not dealt with by the House of Lords: para. 5.55, above.

^M Indeed. he had placcd the onus squarely onto the defendants to show that it was probably not a cause As has already been pointed out (para. 5.56, above,) the Rolam test has nothing to do with this issue: in a vaccine or radiation damage case the burden of proof of causation is not discharged by showing that there is respectable body of medical opinion that the agent may cause such damage or did so in the particular case: Ijooeday v. Rai ton, The Times, March 31, 1988; Reny r. British Nu elear Fuels 119941 5 Med. L.R. 1. But it may be relevant in an indirect way. If, say. D failed to attend a patient who has died, the question may arise of what D would have done if he had attended. If he would have administered a treatment which. with hindsight, would have been effective and that treatment would have been used by any competent doctor his negligence has caused the death; but if he would not have administered the treatment and that decision in the circumstances would have been supported by a responsible body of opinion that is not negligence and the fact that he may have been at fault in failing to attend is not a cause of death: Bolitho v. City and Hackney HA. 119981 A.C. 232 at 240; liryce v. Sutton and Wandsiwrtli HA. (19%) 27 B.M.L.R. 124 at 156. But it seems he is liable if he would have used the treatment even though it would not have been negligent not to do so: ibid.

^ (1987J A.C. 750. On this case and its ramifications, see Stapleton. The Gist of Negligence, Part U” (1988) 104 L.Q.R. 389; Coote, "Chance and the Burden of Proof in Contract and Tort" (1988) 62 A.L.J. 761; Fleming, "Probalistic Causation in Tort Law" (1989) b8 Can. B.R. 661; Hill. "A Lost Chance for Compensation" (1991) 54 M.L.R. 511.

At least this is the way the case was presented. If fact it is a considerable over-simplification. It seems to have represented a conclusion that of a sample of 100 people with a similar injury 25 would have recovered with prompt treatment. But the precise degree of blood vessel damage suffered by C before he entered the hospital was not known. nor will the figurę be known for any of the sample. Some of the 100 would inevitably have suffered the disability whatever was done and the claimant might have been one of those. The point is madę by Lord Mackay in Hotson. See Perry, "Risk, Harm and Responsibility" in Owen (ed.), Philosoyhical Toundations oj Tort Law (1995).