A topic close to my (legal) heart, and one upon which I have been known to speak unprompted at some length, is the correct approach to fact-finding where several possible causes, or causal mechanisms, are suggested for the damage under investigation: a common feature of clinical negligence (and, more widely, personal injury) litigation.

This raises questions relating to the so-called Rhesa Shipping ‘heresy’ – that is, the circumstances in which a court may, or must, decide a case on the burden on proof – and, in some cases, the circumstances in which the ‘doctrine’ of res ipsa loquitur will apply.

This blog considers these questions and ends with some examples of their application in clinical negligence litigation.

The Rhesa Shipping ‘Heresy’

Rhesa Shipping Co v Edmunds concerned a ship, The Popi M, which sank in calm seas and fair weather as a result of a large and sudden entry of water into her engine room through her shell plating. The vessel’s owners claimed against her hull and machinery underwriters, contending that the loss was caused by a peril of the sea or alternatively by crew negligence. The suggested peril of the sea was a moving submerged object i.e. a submarine. The underwriters contended that the vessel was not seaworthy. More specifically, the underwriters advanced a mechanism for unseaworthiness through wear and tear, based on expert metallurgical evidence.

The trial judge, Bingham J, rejected that theory: [1983] 2 Lloyd’s Rep 235. He also rejected the owners’ argument that there had been crew negligence. That left the possibilities that the vessel was in some other way unseaworthy or that it collided with a submarine. At a high level of generality, neither of those explanations would necessarily be hard to imagine. It is far from unknown for vessels to be sent to sea in an unseaworthy state and it is far from unknown for vessels to collide with submersible objects. However, the evidence to support either theory on the particular facts of the case was unsatisfactory, as the experts on both sides candidly recognised.

Bingham J observed that on each side there was recognition that the hypothesis for which that side contended was highly improbable; it was supported as the most likely hypothesis only because any other hypothesis, and in particular the hypothesis advanced by the other party, was regarded as almost (if not altogether) impossible. At p. 245, he said:

Rarely can competing menus have been proffered with such guarded recommendations by each of the chefs responsible.

After setting out cogent reasons why the submarine theory was improbable and his reasons for rejecting the metallurgical argument advanced by the underwriters, Bingham J stated his conclusion at p. 248:

In the result, I find myself driven to conclude that the defendants’ wear and tear explanation must on the evidence be effectively ruled out. That leaves me with a choice between the owners’ submarine hypothesis and the possibility that the casualty occurred as a result of wear and tear but by a mechanism which remains in doubt. Cases must be decided on evidence. My conclusion is that despite its inherent improbability, and despite the disbelief with which I have throughout been inclined to regard it, the owners’ submarine hypothesis must be accepted as, on the balance of probabilities, the explanation of this casualty.

The Court of Appeal upheld Bingham J’s decision and the matter thereafter found its way to the House of Lords.

In his celebrated speech, Lord Brandon of Oakbrook opined, inter alia, as follows [1985] 1 WLR 948, 951-955:

My Lords, the appeal does not raise any question of law, except possibly the question what is meant by proof of a case “on a balance of probabilities.” Nor do underwriters challenge before your Lordships any of the primary findings of fact made by Bingham J. The question, and the sole question, which your Lordships have to decide is whether, on the basis of those primary findings of fact, Bingham J and the Court of Appeal were justified in drawing the inference that the ship was, on a balance of probabilities, lost by perils of the sea.

In approaching this question it is important that two matters should be borne constantly in mind. The first matter is that the burden of proving, on a balance of probabilities, that the ship was lost by perils of the sea, is and remains throughout on the shipowners. Although it is open to underwriters to suggest and seek to prove some other cause of loss, against which the ship was not insured, there is no obligation on them to do so. Moreover, if they chose to do so, there is no obligation on them to prove, even on a balance of probabilities, the truth of their alternative case.

The second matter is that it is always open to a court, even after the kind of prolonged inquiry with a mass of expert evidence which took place in this case, to conclude, at the end of the day, that the proximate cause of the ship’s loss, even on a balance of probabilities, remains in doubt, with the consequence that the shipowners have failed to discharge the burden of proof which lay upon them.

This second matter appears clearly from certain observations of Scrutton LJ in La Compania Martiartu v The Corporation of The Royal Exchange Assurance [1923] KB 650. That was a case in which the Court of Appeal, reversing the trial judge, found that the ship in respect of which her owners had claimed for a total loss by perils of the sea, had in fact been scuttled with the connivance of those owners. Having made that finding, Scrutton LJ went on to say, at p. 657:

This view renders it unnecessary finally to discuss the burden of proof, but in my present view, if there are circumstances suggesting that another cause than a peril insured against was the dominant or effective cause of the entry of sea water into the ship … and an examination of all the evidence leaves the Court doubtful what is the real cause of the loss, the assured has failed to prove his case.

While these observations of Scrutton LJ were, having regard to his affirmative finding of scuttling, obiter dicta only, I am of opinion that they correctly state the principle of law applicable. Indeed counsel for the shipowners did not contend otherwise.

My Lords, the late Sir Arthur Conan Doyle in his book “The Sign of Four”, describes his hero, Mr Sherlock Holmes, as saying to the latter’s friend, Dr Watson: “how often have I said to you that, when you have eliminated the impossible, whatever remains, however improbable, must be the truth?” It is, no doubt, on the basis of this well-known but unjudicial dictum that Bingham J decided to accept the shipowners’ submarine theory, even though he regarded it, for seven cogent reasons, as extremely improbable.

In my view there are three reasons why it is inappropriate to apply the dictum of Mr Sherlock Holmes, to which I have just referred, to the process of fact-finding which a judge of first instance has to perform at the conclusion of a case of the kind here concerned.

The first reason is one which I have already sought to emphasise as being of great importance, namely, that the judge is not bound always to make a finding one way or the other with regard to the facts averred by the parties. He has open to him the third alternative of saying that the party on whom the burden of proof lies in relation to any averment made by him has failed to discharge that burden. No judge likes to decide cases on burden of proof if he can legitimately avoid having to do so.

There are cases, however, in which, owing to the unsatisfactory state of the evidence or otherwise, deciding on the burden of proof is the only just course for him to take.

The second reason is that the dictum can only apply when all relevant facts are known, so that all possible explanations, except a single extremely improbable one, can properly be eliminated. That state of affairs does not exist in the present case: to take but one example, the ship sank in such deep water that a diver’s examination of the nature of the aperture, which might well have thrown light on its cause, could not be carried out.

The third reason is that the legal concept of proof of a case on a balance of probabilities must be applied with common sense. It requires a judge of first instance, before he finds that a particular event occurred, to be satisfied on the evidence that it is more likely to have occurred than not. If such a judge concludes, on a whole series of cogent grounds, that the occurrence of an event is extremely improbable, a finding by him that it is nevertheless more likely to have occurred than not, does not accord with common sense. This is especially so when it is open to the judge to say simply that the evidence leaves him in doubt whether the event occurred or not, and that the party on whom the burden of proving that the event occurred lies has therefore failed to discharge such burden.

In my opinion Bingham J adopted an erroneous approach to this case by regarding himself as compelled to choose between two theories, both of which he regarded as extremely improbable, or one of which he regarded as extremely improbable and the other of which he regarded as virtually impossible. He should have borne in mind, and considered carefully in his judgment, the third alternative which was open to him, namely, that the evidence left him in doubt as to the cause of the aperture in the ship’s hull, and that, in these circumstances, the shipowners had failed to discharge the burden of proof which was on them.

Lord Brandon accordingly concluded, at p. 957, that the judge ought to have found that the ship owners’ case was not proved.

The Scope of the ‘Heresy’

In Ide v ATB Sales Ltd [2008] PIQR P13, having recited the decision in The Popi M, Thomas LJ stated as follows at [4]-[6]:

The Popi M was a very unusual case and as these two appeals demonstrate, the difficulties identified in that case will not normally arise. In the vast majority of cases where the judge has before him the issue of causation of a particular event, the parties will put before the judges two or more competing explanations as to how the event occurred, which though they may be uncommon, are not improbable. In such cases, it is, as was accepted before us by the appellants, a permissible and logical train of reasoning for a judge, having eliminated all of the causes of the loss but one, to ask himself whether, on the balance of probabilities, that one cause was the cause of the event. What is impermissible is for a judge to conclude in the case of a series of improbable causes that the least improbable or least unlikely is nonetheless the cause of the event; such cases are those where there may be very real uncertainty about the relevant factual background (as where a vessel was at the bottom of the sea) or the evidence might be highly unsatisfactory. In that type of case the process of elimination can result in arriving at the least improbable cause and not the probable cause.

In Datec Electronic Holdings v UPS [2007] UKHL 23 ([2007] 1 WLR 1325, [2005] EWCA Civ 1418)) one of the issues was whether the claimants had discharged the burden of establishing on a balance of probabilities that the loss of packages was caused by theft by an employee of UPS. As Richards LJ stated in his judgment at paragraph 67, there was sufficient evidence in that case and the surrounding circumstances to enable the court to engage in an informed analysis of the possible causes of the loss and to reach a reasoned conclusion as to the probable cause. He considered all of the possible causes and concluded that theft by employees was the probable cause of the loss. He concluded at paragraph 83:

Nor do I see any inconsistency between my approach and the observations of Lord Brandon in The Popi M. The conclusion that employee theft was the probable cause of the loss is not based on a process of elimination of the impossible, in application of the dictum of Sherlock Holmes. It does take into consideration the relative probabilities or improbabilities of various possible causes as part of the overall process of reasoning, but I do not read The Popi M as precluding such a course. Employee theft is, as I have said, a plausible explanation and is very far from being an extremely improbable event. A finding that employee theft is more likely than not to have been the cause of the loss accords perfectly well with common sense. Thus the various objections to the finding made by the trial judge in The Popi M simply do not bite on the facts of this case.

On appeal, the approach of Richards LJ was criticised by counsel for UPS on the basis that he had been lured into a process of elimination (which could at best arrive at a conclusion as to which of many possible causes was the least unlikely) rather than a conclusion as to any cause which was more probable than all the others viewed together. In giving the only substantive opinion on this issue, Lord Mance rejected that criticism, though pointing out at paragraph 50 that:

Inevitably, any systematic consideration of the possibilities is subject to a risk that it may become a process of elimination leading to no more than a conclusion regarding the least unlikely cause of loss.

As a matter of common sense it will usually be safe for a judge to conclude, where there are two competing theories before him neither of which is improbable, that having rejected one it is logical to accept the other as being the cause on the balance of probabilities. It was accepted in the course of argument on behalf of the appellant that, as a matter of principle, if there were only three possible causes of an event, then it was permissible for a judge to approach the matter by analysing each of those causes. If he ranked those causes in terms of probability and concluded that one was more probable than the others, then, provided those were the only three possible causes, he was entitled to conclude that the one he considered most probable, was the probable cause of the event provided it was not improbable.

Dealing with matters more broadly in Milton Keynes Borough Council v Nulty [2013] 1 WLR 1183, Toulson LJ opined as follows at [34]-[37]:

A case based on circumstantial evidence depends for its cogency on the combination of relevant circumstances and the likelihood or unlikelihood of coincidence. A party advancing it argues that the circumstances can only or most probably be accounted for by the explanation which it suggests. Consideration of such a case necessarily involves looking at the whole picture, including what gaps there are in the evidence, whether the individual factors relied upon are in themselves properly established, what factors may point away from the suggested explanation and what other explanation might fit the circumstances. As Lord Mance observed in Datec Electronics Holdings Limited v UPS Limited [2007] UKHL 23, [2007] 1 WLR 1325, at 48 and 50, there is an inherent risk that a systematic consideration of the possibilities could become a process of elimination “leading to no more than a conclusion regarding the least unlikely cause of loss”, which was the fault identified in The Popi M. So at the end of any such systematic analysis, the court has to stand back and ask itself the ultimate question whether it is satisfied that the suggested explanation is more likely than not to be true. The elimination of other possibilities as more implausible may well lead to that conclusion, but that will be a conclusion of fact: there is no rule of law that it must do so. I do not read any of the statements in any of the other authorities to which we were referred as intending to suggest otherwise.

The civil “balance of probability” test means no less and no more than that the court must be satisfied on rational and objective grounds that the case for believing that the suggested means of causation occurred is stronger than the case for not so believing. In the USA the usual formulation of this standard is a “preponderance of the evidence”. In the British Commonwealth the generally favoured term is a “balance of probability”. They mean the same. Sometimes the “balance of probability” standard is expressed mathematically as “50 + % probability”, but this can carry with it a danger of pseudo-mathematics, as the argument in this case demonstrated. When judging whether a case for believing that an event was caused in a particular way is stronger that the case for not so believing, the process is not scientific (although it may obviously include evaluation of scientific evidence) and to express the probability of some event having happened in percentage terms is illusory.

[Counsel] submitted that balance of probability means a probability greater than 50%. If there is a closed list of possibilities, and if one possibility is more likely than the other, by definition that has a greater probability than 50%. If there is a closed list of more than two possibilities, the court should ascribe a probability factor to them individually in order to determine whether one had a probability figure greater than 50%.

I would reject that approach. It is not only over-formulaic but it is intrinsically unsound. The chances of something happening in the future may be expressed in terms of percentage. Epidemiological evidence may enable doctors to say that on average smokers increase their risk of lung cancer by X%. But you cannot properly say that there is a 25 per cent chance that something has happened: Hotson v East Berkshire Health Authority [1987] AC 750. Either it has or it has not. In deciding a question of past fact the court will, of course, give the answer which it believes is more likely to be (more probably) the right answer than the wrong answer, but it arrives at its conclusion by considering on an overall assessment of the evidence (i.e. on a preponderance of the evidence) whether the case for believing that the suggested event happened is more compelling than the case for not reaching that belief (which is not necessarily the same as believing positively that it did not happen).

(See also Graves v Brouwer [2015] EWCA Civ 595 at [24]-[25] per Tomlinson LJ.)

Against the background of these authorities, and with characteristic concision, Jackson LJ stated in O’Connor v The Pennine Acute Hospitals NHS Trust [2015] EWCA Civ 1244 at [64]:

It is not an uncommon feature of litigation that several possible causes are suggested for the mishap which the court is investigating. If the court is able, for good reason, to dismiss causes A, B and C, it may be able to reach the conclusion that D was the effective cause. But the mere elimination of A, B and C is not of itself sufficient. The court must also stand back and, looking at all the evidence, consider whether on the balance of probabilities D is proved to be the cause.

The Correct Approach

Drawing the above threads together:

  • It will often be the case that several possible causes are suggested for a particular injury or condition.
  • In such circumstances, if the court is able, for good reasons, to dismiss a number of causes, it must still stand back and consider – on all the evidence – whether the remaining cause or causes are proved on the balance of probabilities.
  • Where the causes are not improbable, it is a permissible exercise for a judge to analyse each cause in turn, adopting a process of elimination, so long as the judge does not merely arrive at the ‘least improbable’ cause.
  • To find the ‘least improbable’ cause proved would be to commit the Rhesa Shipping ‘heresy’.
  • In this connection, it is always open to the court to find that a party has not discharged the burden of proof; indeed, sometimes it is the only course open to the judge.

What About Res Ipsa Loquitur?

In O’Connor, Jackson LJ observed at [59] that a “vast body of case-law” has developed on the topic of res ipsa loquitur.

The classic exposition of the ‘doctrine’ appears in Scott v London & St Katherine’s Docks (1865) 3 H & C 596, 601 per Earle CJ:

There must be reasonable evidence of negligence. But where the thing is shown to be under the management of the defendant or his servants, and the accident is such as in the ordinary course of things does not happen if those who have the management use proper care, it affords reasonable evidence, in the absence of explanation by the defendants, that the accident arose from want of care.

At [60] in O’Connor, however, Jackson LJ stated:

More recent authority has tended to the view that res ipsa loquitur is not a principle of law at all. There is no reversal of the burden of proof. The so-called res ipsa loquitur cases are merely cases in which, on the totality of the evidence, the court was able to make a finding of negligence. It has always been the position that courts can make findings of fact by means of inference when there is no direct evidence of the events in issue.

Then, at [61], Jackson LJ approved the following principles set out by Brooke LJ, with whom Hobhouse LJ and Sir John Vinelott agreed, in Ratcliffe v Plymouth & Torbay Health Authority [1998] PIQR P170, P184, as regards the application of the ‘doctrine’ in clinical negligence cases:

(1) In its purest form the maxim applies where the plaintiff relies on the res (the thing itself) to raise the inference of negligence, which is supported by ordinary human experience, with no need for expert evidence.

(2) In principle, the maxim can be applied in that form in simple situations in the medical negligence field (surgeon cuts off right foot instead of left; swab left in operation site; patient wakes up in the course of surgical operation despite general anaesthetic).

(3) In practice, in contested medical negligence cases the evidence of the plaintiff, which establishes the res, is likely to be buttressed by expert evidence to the effect that the matter complained of does not ordinarily occur in the absence of negligence.

(4) The position may then be reached at the close of the plaintiff’s case that the judge would be entitled to infer negligence on the defendant’s part unless the defendant adduces evidence which discharges this inference.

(5) This evidence may be to the effect that there is a plausible explanation of what may have happened which does not connote any negligence on the defendant’s part. The explanation must be a plausible one and not a theoretically or remotely possible one, but the defendant certainly does not have to prove that his explanation is more likely to be correct than any other. If the plaintiff has no other evidence of negligence to rely on, his claim will then fail.

(6) Alternatively, the defendant’s evidence may satisfy the judge on the balance of probabilities that he did exercise proper care. If the untoward outcome is extremely rare, or is impossible to explain in the light of the current state of medical knowledge, the judge will be bound to exercise great care in evaluating the evidence before making such a finding, but if he does so, the prima facie inference of negligence is rebutted and the plaintiff’s claim will fail. The reason why the courts are willing to adopt this approach, particularly in very complex cases, is to be found in the judgments of Stuart-Smith and Dillon LJJ in [Delaney v Southmead Health Authority (1995) 6 Med LR 355].

(7) It follows from all this that although in very simple situations the res may speak for itself at the end of the lay evidence adduced on behalf of the plaintiff, in practice the inference is then buttressed by expert evidence adduced on his behalf, and if the defendant were to call no evidence, the judge would be deciding the case on inferences he was entitled to draw from the whole of the evidence (including the expert evidence), and not on the application of the maxim in its purest form.

Further Reading: Some Examples

On close analysis of the evidence in O’Connor, the Court of Appeal found that the trial judge had taken care not to commit the Rhesa Shipping ‘heresy’ and had reached his findings on the balance of probabilities without relying on res ipsa loquitur: see [86].

In Collyer v Mid Essex Hospital Services NHS Trust [2019] EWHC 3577 (QB), HHJ Coe QC (sitting as a Judge of the High Court) cited O’Connor and concluded, with evident regret, that it was not possible to identify the cause of the Claimant’s injury, such that he was unable prove his case on the balance of probabilities: see [176].

A further recent example of a clinical negligence claim that failed because it was not proved on the balance of probabilities is Johnson v Williams [2022] EWHC 1585 (QB): see in particular [78]-[86].