Judgments - Dingley v. Chief Constable of Strathclyde Police

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    It seems to me however that the process of reasoning by which they reached these conclusions as disclosed by their opinions was closer together than this summary might suggest. The question to which they had to direct their attention was whether the appellant had proved his case on a balance of probabilities. The matter was complicated by the fact that the critical issues in the case had to be decided by analysing the evidence of expert witnesses who, applying their minds to these issues as scientists, profoundly disagreed with each other about the conclusions which could be drawn from known facts. The standard of proof which they were applying was not that which is applied in civil proceedings by a court. A judge is entitled to find a fact proved if it is established to his satisfaction on a balance of probabilities. This is not a very exacting standard, and the margin on either side of the balance may such that the decision can quite reasonably go either way. It would not be surprising to find that there were differences of view among the judges as to where the balance lay on the first issue which relates to the general question whether trauma can ever cause MS. In these circumstances the process of reasoning, rather than the individual conclusions reached on each chapter, is more important when your Lordships are considering whether the decision as a whole stands up to examination or should be set aside.

    My understanding of the reasons which each of the three judges gave for the conclusions which they reached on the first question is as follows.

    The Lord President noted that there was an obvious conflict between the appellant's witnesses, who referred to a number of cases in their experience where patients previously in good health had developed symptoms of MS after trauma, and the respondent's witnesses, who said that they had not had that experience. He said that the fact that someone like Professor Behan had been able to assemble 16 such cases was something which anyone trying to understand the possible cause of the disease must take into account, as was indicated by the fact that Dr. Poser had been led by similar reports and experiences to put forward the hypothesis that they pointed to a causal relationship between certain traumas and the development of MS plaques and to shape a theory as to why there might be such a causal relationship. But in his view such a hypothesis had to be tested. He proceeded to examine first the epidemiological studies, one of the purposes of which was to test that hypothesis, and then the validity of any theory put forward to explain any assumed relationship between trauma and the development of MS. His conclusion on the epidemiological studies was that they did not support the view that there was a causal relationship between trauma in general and the onset of symptomatic MS, and that this was important because it focused attention on the question whether there was such a relationship between trauma to the spinal cord and the onset of such symptoms. Having examined the theories which were advanced based on the animal experiments, on Gonsette's paper (1966) and on Oppenheimer (1978) he said at p. 601G-H that he did not find it proved, on a balance of probabilities, that trauma in general or whiplash injury in particular could ever trigger the onset of symptoms of MS. He then said that, in view of this conclusion, he did not need to go on to answer the second question. But he observed that he had difficulty in seeing how, even supposing "that it were possible" for trauma to trigger the onset of MS, the evidence established that trauma "was" a trigger in this case rather than coincidental to its onset.

    Lord Prosser said at p. 612 that the account of what happened to the appellant in the accident and of his neck symptoms shortly thereafter seemed to him to show an actual trauma which was at least "quite likely" to show an appropriate injury with damage to the blood brain barrier, and that he would be content to infer that there was indeed such an injury if the general question could be answered in the appellant's favour (my emphasis). This forced him back to the general question, as to which he said that if all one could say in answer to that question was that these cases cannot all be mere coincidence one would lack any positive pointer, in any particular case, as to whether that case was one where the traumatic breach was used by the lymphocytes to penetrate the barrier. Reviewing the evidence on the general question and having noted the discrepancy between the witnesses as to their clinical experience, he said that he accepted that the experience of Professor Behan and Dr. Poser was as they described it and that Oppenheimer's theory sufficed to give an understandable mechanical explanation for the clinical experience. But he found no basis to justify the conclusion that traumatic breach rather than chemical breach was probably the explanation for the symptoms in any particular percentage of cases or more probably than not. That being so, he said at p. 618H that he did not feel able to hold that the appellant "probably" sustained an appropriate injury or, even assuming such an injury, that in this case the traumatic breach rather than chemical breach led to the symptomatic MS. At p. 620 he said that the evidence had in his view established that trauma "can" trigger MS, but that that general conclusion was not enough for the appellant. He could find no basis for treating coincidence as rarer, or as less likely, than traumatic cause in this case.

    Lord Caplan indicated at p. 628 that he was unable to accept the evidence of the appellant's witnesses based on their clinical experience unless it was tested by other evidence. He did not find it possible to find firm support for their evidence from the experiments with animals or in the papers by Gonsette or Oppenheimer. He observed that the precise mechanism for the activation of dormant MS remained unclear. In his view the epidemiological studies had failed to throw up any positive connection between the onset of MS and trauma. As for the nature of the injury which the appellant sustained in the accident, he said at p. 634F that he found the question whether the cervical cord was damaged hard to answer in the abstract as deductions about the nature of that injury were to a degree dependent on the force of any evidence which could establish a recognised link between MS and neck trauma. If it were clearly shown that neck trauma was a recognised facilitator of MS he would be inclined to hold that in the appellant's case the combination of circumstances was not a coincidence, and that the probability was that his neck injury caused MS. But that all depended on it being "probable" that MS could be triggered by neck trauma, which he was unable to find proved.

    It seems to me that Lord Prosser and Lord Caplan were in broad agreement in their approach to the second question. Adopting Lord Prosser's words at p. 612, they would both have been content to infer that the appellant sustained an appropriate neck injury in the accident if they had felt able to hold that symptomatic MS could "probably" be triggered by an injury of that kind. This, as Lord Prosser said, forced them both back to the first or general question, which was the only question that the Lord President found it necessary to answer. As to their conclusions on that question, there was a clear difference of view between the Lord President and Lord Prosser. The Lord President was unable to find it proved on a balance of probabilities that whiplash injury could ever trigger the onset of symptoms of MS, whereas Lord Prosser was satisfied that trauma "can" trigger symptomatic MS. But the significance of this difference is much reduced once one appreciates that the critical question for Lord Prosser was whether it had been proved that traumatic breach was "more probably than not" an explanation for these symptoms. Only if the evidence had persuaded him that this was so would he have been able to hold that in the appellant's case the relationship was more than a coincidence. Agreeing on this point with Lord Caplan, his conclusion was that it had not been proved that trauma was a more probable explanation.

    The significance of the difference of view between the Lord President and Lord Prosser is further reduced by an examination of the views which they expressed about the study which was carried out by Oppenheimer. In what the witnesses on both sides acknowledged to be a paper of high quality, Oppenheimer set out his conclusions after examining the spinal cords in 18 cases of MS. He found that lesions in the cervical cord were more common than at lower levels. In view of their shape and their frequency he expressed the view that mechanical stresses play a part in determining the site of these lesions, and that such stresses are commonly transmitted to the cord during flexion of the spine through the denticulate ligaments. These ligaments run down each of the two lateral aspects of the spinal cord and hold the cord in position within the spine. His conclusion was that in patients with MS neck flexion was dangerous and that patients with the disease should be protected against the effects of full flexion of the head and neck.

    Lord Prosser said at p. 618C that he was persuaded that Oppenheimer's theory sufficed to give an understandable mechanical explanation for the appellant's witnesses' clinical experience. But, as the Lord President pointed out in his detailed analysis of this paper at pp. 594-599 and as Lord Caplan also observed at p. 630, that theory was subject to important limitations. Among these were the fact that he was considering the effects of chronic stress, not sudden trauma such as a whiplash injury, and the absence of any compelling explanation as to why lesions similar to those which he observed in the spinal cord and attributed to movement occur in other areas which are not subjected to movement of that kind. I think, with respect, that much of the force of what Lord Prosser took from this paper is removed by the fact that in his treatment of it he did not subject the paper to the same detailed analysis as the Lord President.

    I have concluded therefore that the outcome of this appeal depends upon what your Lordships are to make of the opinion of the Lord President. The differences between his reasons and those of Lord Prosser on the first question are so marginal in the whole context that the fact that these differences exist does not of itself not serve in any way to undermine the Lord President's opinion on this question, and on all essential matters Lord Caplan agreed with the Lord President. So the appellant must show that the Lord President misdirected himself by approaching the evidence in the wrong way or by failing to understand the nature and significance of that evidence. Only if that hurdle can be overcome would it be open to your Lordships to look at the whole matter afresh and re-examine the question where the balance of probabilities lies on the difficult issues raised by the first question.

The Lord President's opinion

    It has to be said at the outset that the attention to detail and the depth and quality of the analysis which the Lord President brought to bear on the evidence is of such high quality that the task which the appellant has set for himself is a formidable one. Nevertheless it is right to bear in mind that there is an important difference between the exacting standards of thought and analysis which the academic will expect of medical scientists and the task of a judge when he is considering whether the essential elements in a pursuer's case have been established on a balance of probabilities.

    This is not to say that the judge need not examine the detail of the evidence. Of course he must, as his task is to identify the real issues in the case and then determine where the balance lies between the competing positions revealed by the evidence on each side. In a case such as this, an important part of his task is to assimilate and understand the oral and written evidence and to penetrate the arguments which have been developed by the expert witnesses. But when it comes to the point of exercising his judgment on these issues, he must be careful to avoid applying the standard of proof which the expert would apply to them. As Lord President Cooper said in Davie v. Magistrates of Edinburgh, 1953 S.C. 34, 40:

    "Expert witnesses, however skilled or eminent, can give no more than evidence. They cannot usurp the functions of the jury or judge sitting as a jury, any more than a technical assessor can substitute his advice for the judgment of the court."

The function of the judge in a civil case is to decide where the truth lies, or whether the case has been made out, on a balance of probabilities. One cannot entirely discount the risk that, by immersing himself in every detail and by looking deeply into the minds of the experts, a judge may be seduced into a position where he applies to the expert evidence the standards which the expert himself will apply to the question whether a particular thesis has been proved or disproved - instead of assessing, as a judge must do, where the balance of probabilities lies on a review of the whole of the evidence.

    This was a point which clearly troubled Lord Prosser, who introduced his opinion at pp. 602-605 with some general observations on the questions of probability and proof. As he put it at p. 603G-I, he thought it right to labour these issues as he had found it important, and sometimes difficult, to keep bringing them to mind when looking at the evidence of particular witnesses. At the end of this passage, at pp. 604I-605A, he observed that, while a conclusion may seem to be insufficient until one can find an identifiable possible mechanism as a basis for finding that a causal link is proved or established in ordinary or scientific terms, that feeling of insufficiency is much less appropriate if one stops short of such claims and contents oneself with saying that the causal relationship is marginally probable as civil litigation requires. At first sight there is perhaps an indication here that the explanation for the difference of view between the Lord President and Lord Prosser on the first question - although Lord Prosser stopped short of answering that question in a way which would have led him to answer the second question in the affirmative - may have been due to the bringing of different standards of proof to bear on the evidence.

    No doubt with this in view Mr. Mitchell Q.C. for the appellant began his criticism of the Lord President by contending that he had misdirected himself by applying a higher standard of proof, that of scientific proof, to evidence which required to be addressed in terms of a balance of probability. If there were force in this criticism it would go a long way to opening up the whole issue. This would be a misdirection in law which must be taken to have affected the whole of the Lord President's analysis. It is a difficult issue which I have thought it right to examine very carefully.

    The Lord President said that he had had the advantage of reading a draft of Lord Prosser's opinion after he had completed his initial draft, and that Lord Prosser had articulated some of the problems which he himself had experienced. That he was fully alive to the problem is plain from these observations at p. 600:

    "…in their evidence the experts refer at times to a standard of scientific proof which is different from the standard of proof which the court applies when deciding matters of fact. For a court a fact is proved if the court holds that it is more probable than not, even if it is only marginally more probable. By contrast scientific experts will obviously require a much higher standard before they hold that something has been established. I have tried to keep this difference of approach in mind when reaching my conclusion"

    This still leaves the question whether he was successful in that endeavour as he made his way through each chapter of the expert evidence and reached his conclusion at the end of it. But, having read his opinion again and again and having examined for myself much of the evidence, I am unable to detect anything in his opinion which would justify the criticism that he has applied the wrong standard of proof to that evidence. He has undoubtedly subjected all aspects of the appellant's case to a rigorous analysis, especially in those passages where he has insisted that propositions advanced in one part of the evidence must be tested against the evidence which is to be found in other parts. The methods which he has used are well-tried in the field of scientific analysis. The nature of the evidence led on both sides invited that approach to its assessment. But the fact that he has used these methods in order to test the evidence does not persuade me that, at the end of the day, he applied the wrong standard when he came to the point of deciding what had been proved. In my view his opinion is not open to this criticism.

    I turn now to the detailed criticisms of the opinion which Mr. Mitchell developed in the course of his argument. He said that the reasons for the decision on the first question were unsound, that they showed that the Lord President misunderstood the evidence and that the Lord President ought not to have expressed the view which he does at the end of his opinion on the second question without giving reasons for that view.

    The main thrust of Mr. Mitchell's attack on the decision on the first question was that the Lord President did not give proper weight to the clinical and historical evidence in his summing up on this chapter at p. 569E-G. This led him to reject that evidence when testing it against the epidemiological evidence. He ought not to have done this, as the conclusions which he drew from the epidemiological evidence were unsound and unsatisfactory. At p. 585D the Lord President said that the epidemiological studies might not be perfect but that they were the best source of scientific information on the point which was available. But the fact that they were the best source of information that was available was not a sound reason for attaching weight to them in comparison with the clinical and historical evidence. He was right to discount the study by McAlpine and Compston (1952) for the reason given at p. 585F that the figures in that study were built up of many different types of trauma including peripheral trauma. But he should have applied the same reasoning to the Arizona and Mayo Clinic studies, as neither of them had been designed to investigate the specific types of trauma which were said to produce MS plaques. All these studies were subject to the same criticism that they examined a wide range of different types of trauma and were not designed to address the particular point put in issue by the clinical and historical evidence. This had been recognised by Lord Prosser, who said at p. 619B-C that he could not find anything in these studies which threw any useful light on the narrower question as to the specific category of physical injuries which might damage the blood brain barrier. The Lord President accepted at p. 579H-I that weaknesses in Professor Sibley's grasp of the detail of the articles had been revealed in cross-examination. But he then said that the statistical calculations and conclusions should be accepted unless they were actually shown to be wrong. This was an error, as the articles could not speak for themselves and the onus was on the respondent to lead the necessary evidence. The need for evidence of that kind was demonstrated by the Lord President's observation at pp. 580I-581A that the Mayo Clinic study was difficult to follow as its format was not well constructed.

    I think that the answer to these and a number of other detailed criticisms which are set out in the appellant's printed case about the Lord President's treatment of the epidemiological evidence is that the observations to which they were directed must be seen and understood in the context of the Lord President's opinion as a whole. It has not been demonstrated that his narrative of the evidence was inaccurate, and I am not persuaded that he misunderstood the evidence. The question is whether he was entitled to use the evidence as he did, bearing in mind its limitations and the absence of evidence either to support or to undermine the statistical exercises. As regards the statistics, the Lord President was right to point out that the question whether the worked figures were incorrect or overlooked in the analysis was not explored in the evidence. The parties did not join issue on this point. As can be seen from Professor Sibley's cross-examination at pp. 1440C -1445A for example, it was the use to be made of the published material which was in dispute. In these circumstances the Lord President was entitled to proceed upon the basis that the calculations and conclusions should be accepted for what they were worth unless they were shown to be unsatisfactory by contrary evidence, and to concentrate on the use which ought to be made of them. This is in accordance with the usual practice in the treatment of published material which is relied upon by expert witnesses. As regards the use to be made of it, the opinion shows that the Lord President was fully aware of the various criticisms which had been advanced by the appellant's witnesses for disregarding or at least for attaching no significant weight to this material. There was a difference of view between him and Lord Prosser as to the conclusion which was to be drawn from it when it was compared with the clinical and historical evidence. But this of itself does not mean that the Lord President's conclusion at pp. 585C-586D must be rejected as unsound.

    I consider that the views which the Lord President expressed in this passage are fully supported by his careful analysis of the evidence and that he was entitled to reach the conclusions which he did based on that analysis. He was right to point out at p. 586D that the epidemiological studies at least showed that one should look carefully at the evidence which was said to support the existence of a causal relationship between trauma to the spinal cord and the onset of symptomatic MS.

    Mr. Mitchell then turned to the Lord President's treatment of the evidence about experiments on animals, of Gonsette and of Oppenheimer. He said that his reasons for finding that the evidence of the animal experiments did not provide material support for the view that trauma can cause the onset of symptomatic MS were unsound, as this conclusion overlooked the purpose of these experiments. He criticised the Lord President's treatment of the Gonsette paper on the ground that the conclusions which he drew from it at pp. 594B-C and 600F-G were in conflict with evidence given by Professor Behan and Dr. Poser which he had accepted previously. The observation at pp. 598I-599A that Oppenheimer's hypothesis, which involved the effects of movement, did not provide a compelling explanation of why lesions leading to demyelination occurred in areas of the brain which are not subjected to movement of that kind ignored the fact that there was clear evidence that the preponderance of plaques were explicable by movement and the effects of movement. Due to this and other errors in his reasoning the Lord President did not give the weight to Oppenheimer's paper which he should have done.

    Here again I think that the observations which were criticised must be read in the context of the opinion as a whole. Reading them in this way, I am wholly unpersuaded that the Lord President's treatment of these chapters of the evidence was erroneous or than he was not entitled to reach the conclusions which he drew from them. There was an acute conflict between the experts as to the bearing which the experiments on animals had on the question whether trauma can cause the onset of MS in humans. Animals do not develop MS and the condition from which they suffer known as experimental allergic encephalitis is not the same as MS. The weight to be attached to these experiments is a question on which views may differ among experts, but in a civil proof this is a matter for decision by the judge on a balance of probabilities. So also is the question as to the weight to be attached to Gonsette's study of the development of fresh plaques in the vicinity of areas of the brain affected by the procedure known as thalamotomy - the insertion of a trocar, or needle, through the upper layers of the brain through which an electric current is then passed to destroy a part of the brain tissue. At pp. 592-594 the Lord President sets out the evidence from both sides about this study and narrates what the experts on each side had to say about it. He acknowledges the importance of the questions raised by the experiments, and then takes account of the points made in reply by the respondent's witnesses. The conclusion which he reaches at p. 594G that it did not provide a basis for the conclusion that trauma of the kind that the appellant suffered can cause MS seems to me to be fully justified by the careful reasoning which preceded it.

    Similarly, in his treatment of Oppenheimer the Lord President takes full account of the points which have to be borne in mind in doing justice to this study, acknowledges at p. 598G that the paper does indeed suggest that the lateral columns of the spinal cord are a site of preference for the development of MS plaques and accepts that his observations point to a phenomenon that requires to be investigated. At p. 600G he says that, like everyone else involved in the case, he was impressed by this paper and that he accepted that Oppenheimer's hypothesis that breaches of the BBB may be caused by flexion could support the theory that other types of trauma, such as a whiplash injury, could also cause a breach of the BBB leading to demyelination. But in the end, after weighing up all the factors pointing one way and the other, he says at p. 601G that he does not find this theory proved. As regards this part of the case also I am quite unable to find any defect in the Lord President's reasoning to justify the view that he was not entitled to reach this conclusion in the light of his examination of the evidence.


    In the end the process of reasoning which led the Lord President to this conclusion seems to me to be quite straightforward, and in my opinion it is unassailable. There is a body of clinical evidence that shows that there are many cases of symptomatic MS which cannot be related to trauma. In a small number of cases the onset of symptoms is preceded by trauma. That happened in this case, but coincidences can occur. So the theory that trauma triggers the onset of symptoms of MS has to be tested. Experiments on animals and the study by Gonsette show that violence can open up the BBB in such a way as to permit the brain to be attacked by activated and deranged T-lymphocytes. But there was no question of such violence in this case. In any event this evidence still leaves the majority of cases of symptomatic MS unexplained. The epidemiological studies do not support the appellant's case. If anything they tend to support the arguments to the contrary. But for present purposes the important point is that they show that the appellant's case depends upon there being an acceptable theory to explain what it is that overcomes the BBB and permits the development of symptomatic MS. A satisfactory explanation would go a long way to supporting the appellant's case. But the evidence, which reaches its highest point with the study by Oppenheimer, does not go far enough to provide that explanation. So the appellant's case fails on a balance of probabilities.

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