In Kennedy -v- Cordia Services LLP  UKSC 6 the Supreme Court made some telling observations relating to expert evidence. This was in the context of a Scottish case, however the observations are of general importance.
The Supreme Court allowed an appeal and held that breach of duty had been established. The facts of the case are discussed here. It was necessary to consider the role of the expert in the course of the speeches.
THE OBSERVATIONS IN RELATION TO THE ROLE OF EXPERTS
37. Before expressing our views on Mr Greasly’s evidence in this appeal, we look at expert evidence more generally to provide the context for our conclusions. The case law on the Scots law of evidence to which counsel referred included both civil and criminal cases. We refer to both in this judgment but are mindful that the Scots law of criminal evidence, including expert evidence in criminal trials, lies within the competence of the High Court of Justiciary and not this court. In this judgment therefore the criminal cases only provide context for our consideration of the law of evidence in civil cases.
The evidence of skilled witnesses
38. In our view four matters fall to be addressed in the use of expert evidence. They are (i) the admissibility of such evidence, (ii) the responsibility of a party’s legal team to make sure that the expert keeps to his or her role of giving the court useful information, (iii) the court’s policing of the performance of the expert’s duties, and (iv) economy in litigation. The first is the most directly relevant in this appeal. But the others also arise out of either the parties’ submissions or the Extra Division’s concerns and we address them briefly.
39. Skilled witnesses, unlike other witnesses, can give evidence of their opinions to assist the court. This gives rise to threshold questions of the admissibility of expert evidence. An example of opinion evidence is whether Miss Kennedy would have been less likely to fall if she had been wearing anti-slip attachments on her footwear.
40. Experts can and often do give evidence of fact as well as opinion evidence. A skilled witness, like any non-expert witness, can give evidence of what he or she has observed if it is relevant to a fact in issue. An example of such evidence in this case is Mr Greasly’s evidence of the slope of the pavement on which Miss Kennedy lost her footing. There are no special rules governing the admissibility of such factual evidence from a skilled witness.
41. Unlike other witnesses, a skilled witness may also give evidence based on his or her knowledge and experience of a subject matter, drawing on the work of others, such as the findings of published research or the pooled knowledge of a team of people with whom he or she works. Such evidence also gives rise to threshold questions of admissibility, and the special rules that govern the admissibility of expert opinion evidence also cover such expert evidence of fact. There are many examples of skilled witnesses giving evidence of fact of that nature. Thus Dickson on Evidence, Grierson’s ed (1887) at section 397 referred to Gibson v Pollock (1848) 11 D 343, a case in which the court admitted evidence of practice in dog coursing to determine whether the owner or nominator of a dog was entitled to a prize on its success. Similarly, when an engineer describes how a machine is configured and works or how a motorway is built, he is giving skilled evidence of factual matters, in which he or she draws on knowledge that is not derived solely from personal observation or its equivalent. An expert in the social and political conditions in a foreign country who gives evidence to an immigration judge also gives skilled evidence of fact.
42. It is common in Scottish criminal trials for the misuse of drugs for the Crown to adduce the evidence of a policeman who has the experience and knowledge to describe the quantities of drugs that people tend to keep for personal use rather than for supply to others. Recently, in Myers, Brangman and Cox v The Queen  UKPC 40;  3 WLR 1145, the Judicial Committee of the Privy Council approved of the use of police officers, who had special training and considerable experience of the practices of criminal gangs, to give evidence on the culture of gangs, their places of association and the signs that gang members used to associate themselves with particular gangs. In giving such factual evidence a skilled witness can draw on the general body of knowledge and understanding in which he is skilled, including the work and literature of others. But Lord Hughes, in delivering the advice of the Board at para 58, warned that “care must be taken that simple, and not necessarily balanced, anecdotal evidence is not permitted to assume the robe of expertise.” To avoid this, the skilled witness must set out his qualifications, by training and experience, to give expert evidence and also say from where he has obtained information, if it is not based on his own observations and experience.
43. Counsel agreed that the South Australian case of R v Bonython (1984) 38 SASR 45 gave relevant guidance on admissibility of expert opinion evidence. We agree. In that case King CJ at pp 46-47 stated:
“Before admitting the opinion of a witness into evidence as expert testimony, the judge must consider and decide two questions. The first is whether the subject matter of the opinion falls within the class of subjects upon which expert testimony is permissible. This first question may be divided into two parts: (a) whether the subject matter of the opinion is such that a person without instruction or experience in the area of knowledge or human experience would be able to form a sound judgment on the matter without the assistance of witnesses possessing special knowledge or experience in the area, and (b) whether the subject matter of the opinion forms part of a body of knowledge or experience which is sufficiently organized or recognized to be accepted as a reliable body of knowledge or experience, a special acquaintance with which by the witness would render his opinion of assistance to the court. The second question is whether the witness has acquired by study or experience sufficient knowledge of the subject to render his opinion of value in resolving the issues before the court.”
44. In Bonython the court was addressing opinion evidence. As we have said, a skilled person can give expert factual evidence either by itself or in combination with opinion evidence. There are in our view four considerations which govern the admissibility of skilled evidence:
(i) whether the proposed skilled evidence will assist the court in its task;
(ii) whether the witness has the necessary knowledge and experience;
(iii) whether the witness is impartial in his or her presentation and assessment of the evidence; and
(iv) whether there is a reliable body of knowledge or experience to underpin the expert’s evidence.
All four considerations apply to opinion evidence, although, as we state below, when the first consideration is applied to opinion evidence the threshold is the necessity of such evidence. The four considerations also apply to skilled evidence of fact, where the skilled witness draws on the knowledge and experience of others rather than or in addition to personal observation or its equivalent. We examine each consideration in turn.
45. Assisting the court: It is for the court to decide whether expert evidence is needed, when the admissibility of that evidence is challenged. In R v Turner  QB 834, a case which concerned the admissibility of opinion evidence, which Professor Davidson cites in his textbook on Evidence (2007) at para 11.04, Lawton LJ stated at p 841:
“If on the proven facts a judge or jury can form their own conclusions without help, then the opinion of an expert is unnecessary.”
In Wilson v Her Majesty’s Advocate 2009 JC 336, which also concerned opinion evidence, the High Court of Justiciary, in an opinion delivered by Lord Wheatley, stated the test thus (at para 58):
“[T]he subject-matter under discussion must be necessary for the proper resolution of the dispute, and be such that a judge or jury without instruction or advice in the particular area of knowledge or experience would be unable to reach a sound conclusion without the help of a witness who had such specialised knowledge or experience.”
46. Most of the Scottish case law on, and academic discussion of, expert evidence has focused on opinion evidence to the exclusion of skilled evidence of fact. In our view, the test for the admissibility of the latter form of evidence cannot be strict necessity as, otherwise, the court could be deprived of the benefit of a skilled witness who collates and presents to the court in an efficient manner the knowledge of others in his or her field of expertise. There may be circumstances in which a court could determine a fact in issue without an expert collation of relevant facts if the parties called many factual witnesses at great expense and thus a strict necessity test would not be met. In Daubert v Merrell Dow Pharmaceuticals Inc (1993) 509 US 579, the United States Supreme Court referred to rule 702 of the Federal Rules of Evidence, which in our view is consistent with the approach of Scots law in relation to skilled evidence of fact. The rule, which Justice Blackmun quoted at p 588, states:
“If scientific, technical or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise.”
47. The advantage of the formula in this rule is that it avoids an over-rigid interpretation of necessity, where a skilled witness is put forward to present relevant factual evidence in an efficient manner rather than to give an opinion explaining the factual evidence of others. If skilled evidence of fact would be likely to assist the efficient determination of the case, the judge should admit it.
48. An expert must explain the basis of his or her evidence when it is not personal observation or sensation; mere assertion or “bare ipse dixit” carries little weight, as the Lord President (Cooper) famously stated in Davie v Magistrates of Edinburgh 1953 SC 34, 40. If anything, the suggestion that an unsubstantiated ipse dixit carries little weight is understated; in our view such evidence is worthless. Wessels JA stated the matter well in the Supreme Court of South Africa (Appellate Division) in Coopers (South Africa) (Pty) Ltd v Deutsche Gesellschaft für Schädlingsbekämpfung mbH 1976 (3) SA 352, 371:
“[A]n expert’s opinion represents his reasoned conclusion based on certain facts or data, which are either common cause, or established by his own evidence or that of some other competent witness. Except possibly where it is not controverted, an expert’s bald statement of his opinion is not of any real assistance. Proper evaluation of the opinion can only be undertaken if the process of reasoning which led to the conclusion, including the premises from which the reasoning proceeds, are disclosed by the expert.”
As Lord Prosser pithily stated in Dingley v Chief Constable, Strathclyde Police 1998 SC 548, 604: “As with judicial or other opinions, what carries weight is the reasoning, not the conclusion.”
49. In Davie the Lord President at p 40 observed that expert witnesses cannot usurp the functions of the jury or judge sitting as a jury. Recently, in Pora v The Queen  UKPC 9;  1 Cr App R 3, para 24, the Judicial Committee of the Privy Council in an appeal from New Zealand, stated:
“It is the duty of an expert witness to provide material on which a court can form its own conclusions on relevant issues. On occasions that may involve the witness expressing an opinion about whether, for instance, an individual suffered from a particular condition or vulnerability. The expert witness should be careful to recognise, however, the need to avoid supplanting the court’s role as the ultimate decision-maker on matters that are central to the outcome of the case.”
Thus, while on occasion in order to avoid elusive language the skilled witness may have to express his or her views in a way that addresses the ultimate issue before the court, expert assistance does not extend to supplanting the court as the decision-maker. The fact-finding judge cannot delegate the decision-making role to the expert.
50. The witness’s knowledge and expertise: The skilled witness must demonstrate to the court that he or she has relevant knowledge and experience to give either factual evidence, which is not based exclusively on personal observation or sensation, or opinion evidence. Where the skilled witness establishes such knowledge and experience, he or she can draw on the general body of knowledge and understanding of the relevant expertise: Myers, Brangman and Cox (above) at para 63.
51. Impartiality and other duties: If a party proffers an expert report which on its face does not comply with the recognised duties of a skilled witness to be independent and impartial, the court may exclude the evidence as inadmissible: Toth v Jarman  EWCA Civ 1028;  4 All ER 1276, paras 100-102. In Field v Leeds City Council  1 EGLR 54, the Court of Appeal upheld the decision of a district judge, who, having ordered the Council to provide an independent surveyor’s report, excluded at an interim hearing the evidence of a surveyor whom the Council proposed to lead in evidence on the ground that his impartiality had not been demonstrated. It is unlikely that the court could make such a prior ruling on admissibility in those Scottish procedures in which there is as yet no judicial case management. But the requirement of independence and impartiality is in our view one of admissibility rather than merely the weight of the evidence.
52. The Scottish courts have adopted the guidance of Cresswell J on an expert’s duties in The Ikarian Reefer  2 Lloyd’s Rep 68 in both civil and criminal matters: see Lord Caplan in Elf Caledonia Ltd v London Bridge Engineering Ltd September 2, 1997 (unreported) at pp 225-227 and Wilson v Her Majesty’s Advocate (above) at paras 59 and 60. We quote Cresswell J’s summary (at pp 81-82) omitting only case citations:
“The duties and responsibilities of expert witnesses in civil cases include the following:
1. Expert evidence presented to the court should be, and should be seen to be, the independent product of the expert uninfluenced as to form or content by the exigencies of litigation.
2. An expert witness should provide independent assistance to the court by way of objective unbiased opinion in relation to matters within his expertise. An expert witness in the High Court should never assume the role of an advocate.
3. An expert witness should state the facts or assumption on which his opinion is based. He should not omit to consider material facts which could detract from his concluded opinion.
4. An expert witness should make it clear when a particular question or issue falls outside his expertise.
5. If an expert’s opinion is not properly researched because he considers that insufficient data is available, then this must be stated with an indication that the opinion is no more than a provisional one. In cases where an expert witness who has prepared a report could not assert that the report contained the truth, the whole truth and nothing but the truth without some qualification, that qualification should be stated in the report.
6. If, after exchange of reports, an expert witness changes his view on a material matter having read the other side’s expert’s report or for any other reason, such change of view should be communicated (through legal representatives) to the other side without delay and when appropriate to the court.
7. Where expert evidence refers to photographs, plans, calculations, analyses, measurements, survey reports or other similar documents, these must be provided to the opposite party at the same time as the exchange of reports.”
53. In Wilson v Her Majesty’s Advocate (at paras 59 and 60) the High Court of Justiciary quoted the first four duties and added the requirement that an expert witness “should in particular explain why any material relevant to his conclusions is ignored or regarded as unimportant.” In Elf Caledonia Ltd, Lord Caplan quoted Cresswell J’s guidance more fully. In our view, Cresswell J’s guidance should be applied in the Scottish courts in civil cases, making such allowance as is necessary to accommodate different procedures. It is implicit that the seventh duty applies only in relation to items to which the opposite party does not already have access.
54. Reliable body of knowledge or experience: What amounts to a reliable body of knowledge or experience depends on the subject matter of the proposed skilled evidence. In Davie v Magistrates of Edinburgh the question for the court was whether blasting operations in the construction of a sewer had damaged the pursuer’s building and the relevant expertise included civil engineering and mining engineering. In Myers, Brangman and Cox, as we have said, the subject matter was the activities of criminal gangs; a policeman’s evidence, which was the product of training courses and long term personal experience as an officer serving with a body of officers who had built up a body of learning, was admitted as factual evidence of the practices of such gangs.
55. In many cases where the subject matter of the proposed expert evidence is within a recognised scientific discipline, it will be easy for the court to be satisfied about the reliability of the relevant body of knowledge. There is more difficulty where the science or body of knowledge is not widely recognised. Walker and Walker at para 16.3.5 refer to an obiter dictum in Lord Eassie’s opinion in Mearns v Smedvig Ltd 1999 SC 243 in support of their proposition that:
“A party seeking to lead a witness with purported knowledge or experience outwith generally recognised fields would need to set up by investigation and evidence not only the qualifications and expertise of the individual skilled witness, but the methodology and validity of that field of knowledge or science.”
56. We agree with that proposition, which is supported in Scotland and in other jurisdictions by the court’s refusal to accept the evidence of an expert whose methodology is not based on any established body of knowledge. Thus in Young v Her Majesty’s Advocate 2014 SLT 21, the High Court refused to admit evidence of “case linkage analysis” because it was the subject of only relatively recent academic research and a methodology which was not yet sufficiently developed that it could be treated as reliable. See also, for example, R v Gilfoyle  2 Cr App R 5, in which the English Court of Appeal (Criminal Division) refused to admit expert evidence on “psychological autopsy” for several reasons, including that the expert had not embarked on the exercise in question before and also that there were no criteria by reference to which the court could test the quality of his opinions and no substantial body of academic writing approving his methodology. The court also observed that the psychologist’s views were based on one-sided information and doubted that the assessment of levels of happiness or unhappiness was a task for an expert rather than jurors.
(ii) Making sure that the expert performs his or her role
57. It falls in the first instance to counsel and solicitors who propose to adduce the evidence of a skilled witness to assess whether the proposed witness has the necessary expertise and whether his or her evidence is otherwise admissible. It is also their role to make sure that the proposed witness is aware of the duties imposed on an expert witness. The legal team also should disclose to the expert all of the relevant factual material which they intend should contribute to the expert’s evidence in addition to his or her own pre-existing knowledge. That should include not only material which supports their client’s case but also material, of which they are aware, that points in the other direction, viz the court’s concerns about one-sided information in R v Gilfoyle. The skilled witness should take into account and disclose in the written report the relevant factual evidence so provided.
(iii) Policing the performance of an expert’s duties
58. It is not the normal practice of the Scottish courts to hold preliminary hearings or proofs on the admissibility of the evidence of skilled witnesses. Considerations of cost and practicability may often make such a course unattractive. Where the court has significant powers of case management, as in certain actions based on clinical negligence or relating to catastrophic injuries (Rules of the Court of Session 1994 as amended (“RCS”) Chapter 42A), commercial actions (RCS Chapter 47), and intellectual property actions (RCS Chapter 55), a judge can address concerns about the evidence in the report by a skilled witness at a case management hearing and discuss with counsel how they are to be resolved. Wider opportunities for such case management in personal injury actions are likely to result from the implementation of Lord Gill’s Civil Courts Review.
59. In many cases it may not be possible to iron out all difficulties before the proof. A party may object to part or all of a skilled witness’s evidence at the start and during the course of a proof, as occurred in this case. In the absence of objection, the judge should, when assessing whether and to what extent to give weight to the evidence, test the evidence to ascertain that it complies with the four considerations which we have set out in para 38 above and is otherwise sound. In McTear v Imperial Tobacco Ltd 2005 2 SC 1, para 5.17 Lord Nimmo Smith usefully described the judge’s role in these terms:
“[I]t is necessary to consider with care, in respect of each of the expert witnesses, to what extent he was aware of and observed his function. I must decide what did or did not lie within his field of expertise, and not have regard to any expression of opinion on a matter which lay outwith that field. Where published literature was put to a witness, I can only have regard to such of it as lay within his field of expertise, and then only to such passages as were expressly referred to. Above all, the purpose of leading the evidence of any of the expert witnesses should have been to impart to me special knowledge of subject-matter, including published material, lying within the witness’s field of expertise, so as to enable me to form my own judgment about that subject-matter and the conclusions to be drawn from it.”
Lord Brodie referred to this passage in his opinion at para 11. It is not necessary in this appeal to determine how far a court should have regard to published material put to or cited by a skilled witness which is not within his or her core expertise. Much may depend on the nature of the expert’s area of practice, which may or may not involve some working knowledge of related disciplines, and on the centrality of the published material to the matter which the court has to decide: see, for example, Main v McAndrew Wormald Ltd 1988 SLT 141 and, on the analogous question of a medical practitioner consulting another specialist, M v Kennedy 1993 SC 115.
(iv) Economy in litigation
60. In recent years there have been many statements of concern in many jurisdictions about the disproportionate cost of civil litigation. Scotland is no exception. Those concerns include the use of expert witnesses. In the responses to consultation in the Scottish Civil Courts Review some respondents, including the Scottish Legal Aid Board, expressed their concern about the increased reliance on experts in litigation and the consequent cost (Report of the Scottish Civil Courts Review (2009) vol 1, chapter 9, para 64). The latter concern was also discussed in the Taylor Review of Expenses and Funding of Civil Litigation in Scotland (2013), chapter 3, paras 59-95. Cordia in this case challenge what they describe in their written case as “the largely uncontrolled proliferation of experts”.
61. Case management offers a means by which the court can encourage parties to avoid leading evidence on matters which are not contentious, for example by agreeing a statement of fact which explains background matters, which are not the subject of written pleadings, to the court. There may be matters which can readily be agreed, thereby allowing parties’ experts to concentrate on contentious matters. Solicitors with expertise in personal injury actions may use such statements as the basis for agreed evidence in other actions and thereby save expense. Where that is not possible, a court which has case management powers may require experts to exchange opinions, confer and prepare a report which identifies matters of agreement and reasons for any continued disagreement. It can also ascertain the scope for joint instruction of a single expert, and (where it possesses the necessary powers) can exclude expert reports and evidence. Courts also possess powers in relation to expenses which can be used to discourage the excessive use of expert evidence. Nothing that we say in this judgment questions the legitimacy of the underlying concern about reducing the expense of litigation.
RELATED POSTS ON EXPERTS
Permission to call experts
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- Is an expert really necessary? Two recent cases.
- Permission not granted to call employment experts: the relevant principles considered.
- Expert reports: too long and not much use.
- More on experts: non-compliance with the rules taints the evidence badly
- The credibility of witnesses: joint meetings and overreaching experts: a case to point.
- Over eager experts just do not help: they hinder and harm the case of those who call them.
- Beware the expert evidence who “lectures” the court (and tells the judge who to believe).
- Expert evidence about the veracity of witnesses: well, its probably a waste of time.
- An expert must disclose details of professional relationship with a party otherwise the consequences can be dire.
- Irrelevant evidence, inferences and “forgery”: evidential issues in a High Court case.
- Principles of mitigation of loss & the credibility of expert witnesses.
- I didn’t mean it when I signed the joint report: what happens when experts change their minds?
- Expert evidence: the expert’s role: seeing the wood for the trees.
- Cross-examining expert witnesses: hints, tips and links.
- Experts going on a frolic: a family law case where the expert witness was “thoroughly unhelpful”.