Admissibility or weight: what is the test for expert evidence?

The case: The plaintiffs, Mr & Mrs Duffy, claimed to have suffered severe personal injuries as a result of exposure to toxic chemicals present in their home during and after the installation of spray foam insulation. The case had been decided in favour of the plaintiffs and McGee appealed.

Expert evidence: One of the experts was Dr. Thompson, a toxicologist, who came into the case quite late in the day. At the appeal, Collins J added some observations of his own on the issues arising from “the extraordinary evidence that was given at trial by Dr Thompson”.

He began with an account of ‘Expert Evidence in Civil Proceedings’ observing that the domain of expert evidence had expanded inexorably and although it was often indispensable to the just resolution of civil proceedings (and criminal proceedings also) it was “far from being an unalloyed blessing”, adding significantly to the duration and cost of litigation which, as well as being undesirable in itself, could also give rise to concerns regarding equality of arms and access to the courts. He identified another issue of concern as the significant challenge presented by the assessment of the reliability of expert evidence, particularly in the area of complex expert evidence based on novel scientific theories or methodologies, where there was a real risk that the court may inadvertently admit and rely on unreliable evidence is a real one.

Collins J observed that different jurisdictions have taken differing approaches to the issue of reliability. In some jurisdictions reliability is assessed as a threshold admissibility issue. That appears to be the position in the United States (at least at federal level) and in Canada. He cited the influential US Supreme Court decision in Daubert v Merrell Dow Pharmaceuticals (1993) 509 US 579. However, according to McGrath, Evidence (3rd ed; 2020): the “Irish courts have not propounded a test of admissibility which require expert evidence to achieve a specified threshold of reliability before it can be admitted.” Nevertheless, there have been instances in which courts have refused to admit novel scientific evidence because its reliability had not been sufficiently established. Thus, in People (DPP) v Kelly [2008] IECCA 7, [2008] 3 IR 697 the Irish Court of Criminal Appeal rejected evidence based on the CUSUM sequential analysis technique of an inculpatory statement made by the accused because the court was not satisfied that CUSUM had “a properly established scientific provenance or that it has achieved the requisite degree of expert peer approval”.

Even in the absence of a Daubert-style threshold reliability test, the reliability of expert evidence is obviously a crucially important matter. Collins J referred to how in Kennedy v Cordia (Services) LLP [2016] UKSC 6, [2016] 1 WLR 597, the UK Supreme Court identified four considerations governing the admissibility of “skilled evidence”, including “whether there is a reliable body of knowledge or experience to underpin the expert’s evidence”.

Against this background, Collins J then set out the position in Ireland as regards the issue of reliability:

“There is no general requirement that expert evidence must meet any specific threshold of reliability as a condition of admissibility nor do the Irish courts have the “gatekeeping” function contemplated by Daubert. However, in any given case the admissibility of expert evidence may be challenged on the basis that it lacks a reliable scientific or methodological foundation. At what stage of the proceedings, and in what manner, such a challenge should be determined is a matter for case-by-case assessment. Finally, even where admissible, issues of reliability may properly affect the weight to be given to expert evidence.”

He went on to refer to how the weight to be given to evidence, including expert evidence, is always a matter for the court. Ultimately it is always a matter for the court to resolve disputed issues of fact and, while that process may be assisted by expert evidence, the court must not surrender its judgment to experts, however well-qualified they may appear to be.

He then explained to properly perform its function, the court must be able to understand and engage with the evidence, which in turn requires that experts should sufficiently explain their opinions and the basis for them. Their entitlement to express such opinions “is predicated upon also informing the court of the factors which make up their opinion and supplying to the court the elements of knowledge which their long study and experience has furnished to them whereby they have formed that opinion so that, in those circumstances, the court may be enabled to take a different view” (Flynn v Bus Eireann [2012] IEHC 398). It follows that the expert witness must “provide material on which a court can form its own conclusions on relevant issues” (Pora v The Queen [2016] 1 Cr App R 3. Mere assertion or “bare ipse dixit” on the part of the expert witness is, accordingly, “worthless” (Kennedy v Cordia (Services) LLP [2016] UKSC 6, [2016] 1 WLR 597).

Collins then pointed out that the most significant concern about expert evidence relates to issues of objectivity, impartiality (lack of bias) and independence, noting that concerns of that kind prompted Cresswell J to formulate a detailed statement of the duties and responsibilities of expert witnesses in civil proceedings in The Ikarian Reefer [1993] 2 Lloyds Rep 68.

This led him to say that the legal practitioners acting for a party seeking to adduce expert evidence bear an important responsibility for ensuring that the evidence is relevant and likely to assist the court and that witness has the necessary expertise to give it. They must also ensure that such evidence is confined to issues properly within the scope of the expert’s relevant expertise. They also have a duty to ensure – and this is critical – that the witness fully understands, and is in a position to comply with, the duties of an expert witness, as articulated in the jurisprudence and encapsulated in procedural rules such as, in Ireland, Order 39, Rule 57(1). If not, the witness should not be proffered.

Referring to the observation of Noonan J in the judgment in the instant case he said that unfortunately it is evident that many expert witnesses either fail to understand and/or fail to take seriously their duties as such. Far too frequently, expert witnesses appear to fundamentally misunderstand their role and wrongly regard themselves as advocates for the cause of the party by whom they have been retained. It may be said that this is an established part of litigation culture in this jurisdiction. If so, the culture is unacceptable and it needs to change. To that end, courts need to be forceful in policing the rules and in taking appropriate measures where those rules are not complied with.

Any significant departure from the essential requirements of objectivity, impartiality and independence must be taken very seriously. There was considerable debate in this case as to whether such matters went only to weight or whether a want of objectivity, impartiality or independence might reach the point where the evidence of an expert should be excluded altogether. Collins J had no hesitation in concluding – in agreement with Noonan J – that, as a matter of principle, (lack of) objectivity, impartiality and independence may (and in an appropriate case will) go to the admissibility of expert evidence, not merely to the weight to be given to such evidence.

Where it appears that an expert is unable and/or unwilling to comply with his or her duty to give objective, impartial and independent evidence – as was the position here with Dr  Thompson – then in the view of Collins J their evidence should ordinarily be excluded as inadmissible. He took this formulation from the judgment of the Supreme Court of Canada in WBLI v Abbott and Haliburton 2015 SCC 23, [2015] 2 SCR 182 and after reviewing that judgment he added that where it is evident that an expert witness is either unwilling or unable to comply with their duties as expert, their evidence can - and ordinarily should - be excluded as inadmissible. He said that he was not referring to minor transgressions, which may properly be seen as going only to weight. Rather, he was speaking of significant departures from the fundamental requirements of objectivity, impartiality and independence. He then turned to Dr Thompson:

"While it may be that it will sometimes be difficult to draw the dividing line, no such difficulty arises here in my view. Regrettably, Dr Thompson demonstrated a total lack of understanding of, or respect for, the duties of an expert witness in this jurisdiction.”

He then made some observations simply by way of emphasis of the many difficulties that had been identified by Noonan J in his judgment in the instant case:

• Dr Thompson’s written report, while not evidence in itself, contained numerous “red-flags” indicating the approach he was likely to take in his evidence. These red-flags included:

​

1. Dr Thompson – who is a toxicologist, not a lawyer, expressing views about the doctrine of res ipsa loquitur;
2. Dr Thompson purporting to make categorical statements about disputed issues of fact about which he had no independent knowledge;
3. Dr Thompson accusing the plaintiffs of “misrepresentations” of the installation process;
4. Dr Thompson purporting to identify “contradictions” in the plaintiffs’ accounts;
5. Dr Thompson – who, again, is a toxicologist, not a respiratory physician doctor - suggesting that the plaintiffs had not told their treating doctors, including Professor Burke, “the full truth about their injuries or illnesses”, suggesting that Professor Burke had been misled by the information provided to him into making “false exposure assumptions”, purporting to comment generally on the opinions expressed by Professor Burke in his reports and purporting to express a view (in trenchant terms) as to the cause of the plaintiffs’ respiratory inflammation which contradicted the views of Professor Burke;
6. Dr Thompson – who, again, is a toxicologist and not a psychiatrist – purporting to comment on the views expressed in the psychiatric reports which had been exchanged by the parties and
7. Dr Thompson purporting to express his views on the contents of medical reports prepared by the plaintiffs’ family doctor addressing local skin irritations which the plaintiffs had presented with and going to present an “alternative exposure and causation assessment”. More generally, the tone of absolute certainty that is evident throughout the report, and the aggressively dismissive attitude taken by Dr Thompson to any information that might suggest that the plaintiffs had indeed been negligently exposed as claimed, should perhaps have given rise to concern.

• In light of the features briefly identified above, it is rather surprising that it was considered appropriate to serve Dr Thompson’s report in the form it was served. It is equally surprising that the report did not provoke any objection from the Plaintiffs to Dr Thompson being called.

• When called, Dr Thompson seriously abused his position as expert witness to repeatedly accuse the plaintiffs of outright dishonesty and deception, in circumstances where – as already observed – he had no independent knowledge of the facts and no role whatever in resolving any conflicts of fact as between the parties (and where his allegations were, in any event, contradicted by the factual evidence). In my view, this aspect of Dr Thompson’s evidence, even if it stood alone, was more than sufficient to disqualify him as an expert.

• Of course, it did not stand alone. Numerous other factors are identified by Noonan J in his judgment and I agree entirely with his observation that any of those matters on its own would strongly suggest a lack of objectivity and impartiality on Dr Thompson’s part but that, taken together, they can only be described as “a wholesale abdication” by him of his duties as an expert witness.

• I agree in particular that Dr Thompson’s reliance on the two Wood papers, which were industry-generated and which had not been peer-reviewed (and which, in any event, as Noonan J notes, were primarily concerned with ventilation, whereas Dr Thompson repeatedly asserted that the issue of ventilation was irrelevant) and his adamantine refusal to engage appropriately with any of the documentary material that was inconsistent with his thesis that it was scientifically impossible that the plaintiffs had been exposed to isocyanate on the basis (so he said) that there was no risk of exposure after a period as short as 30 minutes (material including the Icynene Inc safety data sheets, the EPA and other regulatory documents put to him in cross-examination, as well as the two documents cited in the bibliography to his report which were discussed at length in cross-examination) clearly indicated that Dr Thompson was acting as partisan advocate, clinging at all costs to an evidential thesis that, however implausible, would exonerate his client if only the court might be persuaded to accept it.

• Similarly, Dr Thompson’s insistence that any respiratory injury suffered by the plaintiffs was caused by exposure to fibreglass, in the teeth of the very clear evidence to the contrary given by Professor Burke significantly undermined his objectivity, impartiality and independence.

• I also agree that issues arise as to the reliability of the Wood papers, given their provenance, the limited nature of the experimental data involved and the fact that they appear not to have been subject to either pre- or post- publication peer review. Peer review “is an important but fallible filter, which tries to exclude from publication material that is trivial or uses flawed methods or draws conclusions unjustified by the tests used” (Ogden, “Lawyers Beware! The Scientific Process, Peer Review and the Use of Papers in Evidence”, (2011) 55 Ann Occup Hyg 689). In truth, however, much the larger problem here was Dr Thompson’s misuse of the Wood papers, rather than the actual content of those papers.

Collins J concluded that in these circumstances, the Judge was perfectly entitled to make the findings that he did about Dr Thompson’s evidence. The manner in which Dr Thompson had given his evidence clearly demonstrated that he was unable or unwilling to comply with his duties as an expert witness. Accordingly, he was not qualified to give expert opinion evidence and the evidence that he did give had to be disregarded in its entirety as inadmissible. The fundamental frailties of that evidence went far beyond anything that could properly be addressed merely by discounting the weight to be attached to it. The Judge would have been seriously in error had he adopted such an approach.

Finally, Collins J said that this was:

“a disturbing case and it is certainly to be hoped that its like will not be seen again. As I have said, there needs to be a significant change of culture in this area. As well as the duties of expert witnesses themselves, I emphasise again the responsibilities of legal practitioners. The adverse consequences of calling an expert witness who is unable or unwilling to comply with their duties as such may not necessarily be limited to the exclusion of their evidence, serious as that may be for the party concerned. It may also have adverse consequences in costs.”

Commentary: As in Ireland, courts in the other jurisdictions in the British Isles do not mandate a Daubert-style threshold reliability test as applied in the US. As Hodgkinson and James (Expert Evidence: Law and Practice. (4^th edn.) Sweet & Maxwell, 2015; p.31) comment, ‘the most effective way of assessing expertise is, rather than conducting a difficult exercise based almost entirely upon the limited evidence as to qualification, experience and skill at the admissibility stage, to hear the witness’s substantive evidence and use this as the basis upon which to judge not only the quality of his evidence, but his competence to give it.’ However, in an exceptional case, as here, where the expert singularly and spectacularly fails in their duties to the court, expert evidence may be deemed inadmissible and never get to the stage of being tested for weight.

Learning points:

• Ensure that your evidence is not open to challenge on the basis that it lacks a reliable scientific or methodological foundation
• Be able sufficiently to explain your opinions and the basis for them informing the court of the factors which make up your opinion and supplying to the court the elements of knowledge which your long study and experience has furnished you
• Leave debate about legal doctrines to the lawyers
• Do not give evidence outside your field of expertise
• Do not make categorical statements about disputed issues of fact about which you have no independent knowledge
• Be careful about identifying “contradictions” in witnesses’ or litigants accounts unless they would only be identifiable with expert knowledge
• An aggressively dismissive attitude towards the pleaded case may reduce the weight that is attached to your evidence
• Avoid accusing litigants of outright dishonesty and deception in circumstances where you have no independent knowledge of the facts and no role whatever in resolving any conflicts of fact as between the parties
• Beware reliance on publications which are industry-generated and which have not been peer-reviewed