Expert Evidence: The Judiciary’s Approach and Experience under the
Rules of Court 2021 (1)
21 November 2023
The Honourable Justice Kannan Ramesh
Supreme Court of Singapore
Professor Leslie Chew, Senior Counsel, Dean, School of Law, Singapore University of Social Sciences,
Mr Gregory Vijayendran, Senior Counsel,
Ladies and Gentlemen
1. A very good morning to all of you. It gives me immense pleasure to be invited to deliver the keynote address for this year’s Asia Pacific Institute of Experts Symposium. I am most grateful to the organisers for the invitation, and I congratulate and commend them for organising this event on the very important subject of experts and expert evidence.
2. The use of expert evidence in dispute resolution has been the subject of sharp focus in recent years. There are several reasons for this, but one does stand out. And that is because the parties, and indeed the experts, at times lose sight of the real purpose of expert evidence. There are two aspects to this. First, whether expert evidence is even relevant and necessary. Second, experts failing to adhere to their duties to the court. On the first, evidence is principally about facts, with opinions being generally treated with a degree of circumspection. However, expert opinion is an exception to this. Experts play a crucial role in assisting the court on issues that require specialised knowledge on which they have the requisite training, study or experience. Thus, whether expert testimony is necessary is a threshold question. This question is often forgotten in the adversarial fray. On the second, the expert’s duty to the court is paramount. This is a touchstone of expert testimony. The increasingly adversarial nature of expert evidence has led in some instances to a disengagement from this duty and several unwanted consequences, namely partisanship, disproportionate costs, excessive delays and the obfuscation of issues. Therefore, to harness the true value of expert evidence, it is vital that we return to the fundamentals. How do we chart the way forward? I suggest that the new Rules of Court 2021 (“the new Rules”) offers a roadmap for the future. In my view, the new Rules have reshaped the paradigm of expert evidence in civil litigation.
3. I unpack my presentation in three parts. I begin by contextualising the importance of expert evidence with reference to the neutrality of expert witnesses and the court’s approach to evaluating expert opinion. I will then consider the procedural tools that were in place in the Rules of Court (2014 Rev Ed) (“the 2014 Rules”) to facilitate an efficient presentation of expert evidence. I do so to set the backdrop for the third and concluding part of my presentation, namely the sea of change brought about by the new Rules.
Part 1: The Neutrality of Expert Witnesses and the “Basis Rule”.
4. I start with the neutrality and ethical compass of the expert. This is interlaced with the expert’s paramount duty to the court. The expert must never lose sight of this as to do so undermines the administration of justice. This duty overrides any obligation to the person who instructs the expert or by whom he is paid(2). The primacy of this duty is underscored by the requirement that the expert acknowledges the duty in his affidavit and report(3). An expert witness is therefore expected to be impartial and detached from the fray, without any interest in the outcome of the proceedings(4). These are inviolable requirements.
5. However, in practice, there is a real risk that an expert’s neutrality may be swayed. There are various reasons for this. The first is an obvious one. An expert witness is retained to advance a party’s case and may be caught up in the cause of that party. Second, the expert may have a historical and longstanding relationship with the party or its affiliates in various capacities, including engagements in other disputes. Third, there may be prospects of future engagements by the party or its affiliates(5). In isolation or combination, these factors may cloud the expert’s judgment, subtly or otherwise, which could result in actual bias. At the very least, they lay the ground for a suspicion or an allegation of apparent bias. This must be guarded against assiduously.
6. Concerns over bias and partisanship have caused sharp rebukes by the courts in a series of cases in the last decade(6). I highlight two to illustrate. In Wong Meng Cheong v Lin Ai Wah  1 SLR 549, which involved a family dispute over the transfer of property, the plaintiff called two experts to testify on the transferor’s mental capacity at the time of the transfer. The High Court found that the plaintiff’s experts failed to disclose their “fairly close relationship” with the plaintiff, and demonstrated “partiality to the plaintiff’s case … by being selective in the presentation of the relevant medical evidence”(7).In Mehra Radhika v Public Prosecutor  SGHC 214, a judgment of the Chief Justice, the appellant, who was charged with an offence of arranging a marriage of convenience, sought to adduce a medical report which opined that she had depression. The Chief Justice noted that the medical report was “patently lacking in objectivity with a great portion attempting to set out background facts that were exceedingly favourable to the appellant”. The Chief Justice also stated that the report was “plainly erroneous in stating that the appellant had been used in a marriage for visa scam without her knowledge” when it had been shown that the appellant knew exactly what she was doing(8).
7. These cases were unfortunate manifestations of experts losing sight of their duties in an adversarial setting. The judgments serve as a signal reminder of the standards that are expected of experts in terms of neutrality and objectivity. As I will elaborate later in my address, the new Rules go some distance in answering these concerns.
8. I move from neutrality and objectivity to a related consideration. As part of his duty to the court, the expert must ensure that his opinion rests on an accurate bedrock of facts. An expert’s opinion is shaped by the instructions and facts on which it is based. If the facts relied upon by the expert are inaccurate or incomplete, or if the instructions given to the expert do not paint the whole picture, the opinion is undermined. This leads me to the “basis rule”.
9. As Heydon J famously held in Dasreef Pty Ltd v Hawchar  HCA 21 at , “Opinion evidence is a bridge between data in the form of primary evidence and a conclusion which cannot be reached without the application of expertise. The bridge cannot stand if the bedrock of primary evidence does not exist or cannot withstand scrutiny(9). Thus, where the facts undergirding an expert’s opinion are not placed before the court or rejected at trial, the expert opinion may be cast in doubt or rejected entirely. This is the “basis rule”.
10. The “basis rule” requires that an expert's opinion be firmly rooted in credible and admissible evidence. This is perhaps best illustrated by criminal matters, specifically as regards psychiatric evidence. In such cases, an expert’s medical opinion is usually based on an accused person’s self-reported symptoms. As the diagnostic criteria of many mental diseases and disorders are widely available on the Internet, this poses a real risk that an accused person may exaggerate or malinger symptoms to procure a favourable medical assessment(10).
11. The “basis” rule therefore requires that the accused adduces evidence as to the relevant factual basis of the medical opinion. Only then can the psychiatrist’s opinion be properly assessed(11). As part of his duty to the court, it is the responsibility of the expert to ensure that such facts exist to support his opinion.
12. This was the situation in Anita Damu v Public Prosecutor  3 SLR 825. The accused there committed various acts of abuse against her domestic helper. She pleaded guilty but asserted in mitigation that she suffered from Major Depressive Disorder (“MDD”). Her expert opined that the accused was experiencing auditory hallucinations when she committed the offences. Notably, the accused did not give evidence of this at the Newton hearing. The Chief Justice found that the issue of whether the accused was experiencing auditory hallucinations at the material time was a purely factual question that should have been resolved by direct evidence from the accused(12). As the expert’s opinion was based on what the accused had told him which was not established in evidence,(13) the Chief Justice found that the expert’s evidence was “critically undermined” and consequently gave it no weight(14).
13. I segue here to point out the distinction made in Anita Damu between “specific hearsay” and “general hearsay”. I do so because the basis rule requires the facts relied upon to be both credible and admissible. Anita Damu itself was about “specific hearsay”. The expert in that case relied on the accused’s self-reported symptoms to testify as to the primary fact of auditory hallucinations. This was “specific hearsay” and inadmissible because the accused person did not testify to that fact and the expert had no personal knowledge of the same. “Specific hearsay” must be distinguished from “general hearsay”. General hearsay is information and knowledge which the expert has acquired from various sources during his career, such as from authoritative publications or other extrinsic materials customarily employed in the expert’s line of work. This distinction is important because, the full rigour of the hearsay rule is relaxed where the expert’s opinion is based on “general hearsay”— it would be a herculean task for a party to adduce direct evidence of the truth of all the information which the party’s expert has accumulated in the course of his career(15).
14. An illustration of this distinction can be found in the valuation proceedings in the Singapore International Commercial Court case of Kiri Industries Ltd v Senda International Capital Ltd  3 SLR 125 (“Kiri”). In that case, the court found Senda to have engaged in oppressive conduct against Kiri and ordered Senda to purchase Kiri’s shares in DyStar, their joint venture vehicle. Senda’s expert and Kiri’s expert arrived at vastly different valuations of the shares. A key disagreement was whether Kiri’s expert was entitled to rely on market reports and forecasts, based on published information, of selected comparable companies to justify her valuation. Senda objected to the admissibility of these on the grounds that they were hearsay, and that their makers were not called as witnesses.
15. The majority in Kiri adopted the distinction in Anita Damu between “specific hearsay” and “general hearsay”. The majority concluded that the reports and forecasts were materials customarily relied upon in valuation exercises and therefore constituted “general hearsay”(16). As these documents were adduced as evidence of the market’s prognosis for comparable companies and not to prove the truth of the underlying data, they were “general hearsay”(17). On the other hand, the minority found that these documents were “specific hearsay” because they contained historical data of these companies which Kiri’s expert had no personal knowledge of. Nevertheless, the minority concluded that the documents were admissible as an exception to the hearsay rule in the Evidence Act being records of a trade, business or profession(18).
16. Having addressed neutrality and the “basis rule”, I turn my presentation to the court’s approach to evaluating expert evidence. The focus here is on a comprehensive evaluation of the expert’s analytical process. The case of Public Prosecutor v Teo Ghim Heng  SGHC 13 illustrates this. This was a tragic case of double homicide where the accused murdered his wife and only child, his daughter. The accused relied on the defence of diminished responsibility on the basis that he was suffering from MDD (Moderate) at the time of the offences. Both experts agreed that the DMS-V was the applicable diagnostic criteria for MDD, but arrived at opposite conclusions. The accused’s expert testified that the accused suffered from MDD (Moderate). The Prosecution’s expert strongly disagreed. Faced with this strident disagreement, the court evaluated the diagnostic criteria for MDD in DMS-V, identifying as relevant symptoms depressed mood for most of the day, diminished interest or pleasure in all aspects of life, and diminished ability to think or concentrate. The court found that these symptoms were not made out when tested against the factual evidence. The testimony of the accused’s colleagues, ex-colleagues and family members did not suggest that he was depressed for most of the day. The evidence instead showed that the accused was positive, motivated, and kept a meaningful and productive schedule in many aspects of his life. He did not lose interest in his work, and was loving towards and cared for his family(19). The accused’s post-homicide conduct was also pertinent. The fact that he had the presence of mind to forge his wife’s suicide note and to lie to the police when arrested that they had a suicide pact, spoke to his ability to concentrate, think and plan(20). Consequently, the court rejected the opinion of the accused’s expert which was based on the accused’s self-reported symptoms. The decision was subsequently upheld on appeal by the Court of Appeal on broadly the same grounds(21).
17. A similar analysis was undertaken in Ilechukwu Uchechukwu Chukwudi v Public Prosecutor  1 SLR 67. There, the accused was charged with trafficking in not less than 1,963.3g of methamphetamine from Nigeria into Singapore in a piece of black luggage. He told several lies to the police after his arrest, including that he had only brought a laptop bag into Singapore. The accused was initially convicted by the Court of Appeal(22) but when the matter was remitted to the High Court for sentencing, fresh and material evidence came to light that the accused suffered from PTSD, with dissociative symptoms. One of the experts testified that the accused suffered from PTSD because of his childhood trauma from witnessing the Wukari massacre in Nigeria. This potentially explained why the accused perceived his arrest as life-threatening and lied in his statements to save his own life. In determining whether to set aside the conviction, the Court of Appeal undertook a thorough analysis of the DSM‑5 PTSD Criteria. The majority of the Court of Appeal found that because of his childhood trauma in witnessing the Wukari massacre, the accused’s subjective perception of the arrest might differ from a rational person(23). On the facts, the court found that the accused perceived his arrest and his being informed of the death penalty as life-threatening(24). These constituted traumatic events under the DMS-5 PTSD Criteria which would have triggered his PTSD symptoms. This was also consistent with how the accused had vividly described his arrest using words such as “war”, “control” and “chaos” at the trial, long before any issue relating to his conditions was raised(25). The majority therefore found that there was a credible connection between the accused’s condition and his lies and omissions in his statements, and set aside his conviction(26).
18. The cases I have touched on illustrate the degree of scrutiny that the courts adopt in evaluating expert opinion. This ameliorates the concerns over bias and partisanship but does not address them fully. It also does not address the problems associated with costs and delays arising from expert evidence. These issues have been addressed to a large extent by the new Rules. However, to appreciate the impact of the reforms, it is important to first understand the tools in the 2014 Rules which the new Rules have supplemented or improved upon. I turn to this next.
Part 2: Expert conferencing and “hot-tubbing”
19. I highlight two procedural tools in the 2014 Rules that are most pertinent. The first is expert conferencing and joint expert reports. The court could, at any stage, direct a conference between experts to discuss and agree on a list of relevant issues(27). The court could also direct the experts to submit a joint report which listed their points of agreement and disagreement in the shape of a Scott Schedule(28). Expert conference ensured that there was a degree of joinder of issues so that the party’s experts were not at cross-purposes. The Scott Schedule delineated the scope of the issues in contention providing a picture of the areas of consensus and disagreement. Overall, this tool, at least on paper, improved efficiency in the presentation of expert evidence.
20. However, the reality was at times different. Where the experts had fundamental differences in methodology or analysis, the expert conference served only to harden positions, and the joint report was nothing more than another piece of paper evidencing their intractable differences. Where this was the case, the cost advantages associated with expert conferences and joint reports were more apparent than real.
21. A second procedural tool was the concurrent presentation of expert evidence. The court could, subject to the parties’ consent, order expert witnesses to testify as a panel. This is commonly known as “hot-tubbing”.
22. “Hot-tubbing” is to be contrasted with the traditional method of cross-examination where each party’s counsel will cross-examine the other party’s expert when they present their respective evidence. Under the traditional model, the sequential manner in which expert evidence is presented may result in the court not having the benefit of the views of the other party’s expert on the responses given by his counterpart under cross-examination. “Hot-tubbing” addresses this problem by enabling experts to respond to their counterpart’s views “real time”, allowing differences to be tested on the spot. The added and significant advantage of this is that the testing of expert evidence is not left solely to the cross-examiner since it is open to the experts to challenge each other’s views almost instantaneously. “Hot-tubbing” also ensures that the experts present their opinion on an issue-to-issue basis which allows the court to delve into the differences more effectively. This is especially helpful in complex cases where it may be difficult to appreciate the nuances in the dispute solely from the witness statements, expert reports, and cross-examination(29).
23. However, under the 2014 Rules, “hot-tubbing” could only be used with the parties’ consent(30). Even where the parties consent, its effectiveness depended heavily on the interactions between the experts on the stand. I cite three reasons why this was so. First, an expert who was naturally more vocal or charismatic might dominate the discussion, not because of the merits of his opinion, but because he was not rebutted by a less charismatic or vocal witness. It was then left to the cross-examiner to ensure equality of arms which might or might not happen. Second, there might be situations where one expert exerts influence on the other, whether due to seniority, language proficiency, cultural factors, or a pre-existing professional relationship(31). Third, unfriendliness or hostility between experts, and in extreme cases, exchanges of insults can derail the adjudication process(32).
24. It must be readily apparent that the shortcomings of the tools I have described are largely a result of the adversarial use of expert evidence. This raises a key question: is the adversarial approach the best way to harness the benefit of expert evidence in civil litigation? This sets the stage for a discussion on the changes brought about by the new Rules.
Part 3: The Shift in Paradigm Brought by the New Rules of Court 2021
25. I started my address by highlighting the concerns expressed over expert evidence, and unpacked the issue with reference to two aspects, namely the relevance and necessity of expert evidence, and bias, obfuscation of issues, delay and costs. I suggest that the new Rules have met these concerns head-on and found solutions. These solutions represent a paradigm shift in our treatment of expert evidence.
26. After several years of detailed consultations and careful deliberations, the new Rules were gazetted in December 2021. Notably, the effective date of the Rules was pushed back to 1 April 2022 to allow the Bar time to assimilate the changes given their significance. The five ideals that underpin the new Rules are encapsulated in O 3, r 1: (a) fair access to justice; (b) expeditious proceedings; (c) cost-effective work proportionate to the matter; (d) efficient use of court resources; and (e) fair and practical results suited to the needs of the parties. These ideals foreshadow the shift from the adversarial model in the use of expert evidence, to a model which confers on the court control over the deployment of expert evidence(33). I highlight four features.
27. First, party autonomy to decide whether expert evidence is required has been removed. Expert evidence may only be used if the court approves(34).And, the court must not approve unless the expert evidence will contribute materially to the determination of any issue in the case and that issue cannot be resolved by submission or the parties’ agreement. These changes set aside the default position under the 2014 Rules that the parties are prima facie entitled to adduce expert evidence if the requirements for admissibility are met(35). By imposing a leave requirement, the court is given control on whether expert evidence is required and on what issues. It is immediately obvious that the potential for wastage of costs and delay arising from indiscriminate use of expert evidence is curtailed if not eradicated.
28. Second, the court can disallow or reject the use of expert evidence if it finds that the expert lacks the requisite specialized knowledge, or if the expert lacks impartiality(36). It cannot be gainsaid that an expert must have the requisite specialised knowledge on the issues at play and must be clear of conflict(37). The parties are therefore compelled to be circumspect in identifying expert witnesses who have both the necessary qualification and a clean bill of health. This reinforces the duty of the expert to the court and the purpose of expert evidence.
29. Third, to the extent possible, the parties must agree on a common expert(38). Further, save in limited circumstances and subject to the court’s approval, there shall only be one expert on any issue(39). Finally, the court must give all appropriate directions relating to the appointment of the experts including the remuneration to be paid(40).
30. I segue here briefly to make the point that the obligation of the parties to agree on a common expert represents a foundational shift from the previous adversarial approach and harkens back to the purpose of expert testimony. By requiring the parties to endeavour to agree on a common expert, two issues are addressed. First, the problem of bias or partisanship, and the parties treating their experts as “hired guns”. Second, the parties are prevented from treating expert evidence as an “arms race”, thereby minimising costs and delays in civil litigation. Importantly, the playing field for less financially capable parties is levelled or at least improved by ensuring that expert testimony is only resorted to if necessary, with the costs associated with it controlled by the court. This undoubtedly promotes access to justice.
31. I hasten to add that the new Rules do not mandate that a common expert must be used in every case. The parties are only required to agree “as far as possible” to the use of a common expert. In special cases, the court may allow the parties to rely on their own experts on any issues after considering their views, the cost proportionality and whether evidence from a party’s expert is necessary to reach a just outcome(41). Also, the court is empowered to appoint a court expert in addition to or in place of the parties’ common expert or all the experts(42). This gives the court flexibility to account for the different needs of each case.
32. Where a common expert is not considered appropriate, the court is empowered to order meetings between the parties, their solicitors, and their experts to narrow the dispute and agree on the issues to be referred to the experts. Also, the court may order the experts to testify as a panel. This reinforces the “hot-tubbing” procedure in the 2014 Rules, the key difference being the court’s ability to direct the experts to testify concurrently without the parties’ consent(43).
33. Fourth and finally, the parties must agree on a list of issues to be referred to the experts and significantly, subject to the approval of the court, a common set of agreed or assumed facts that the experts will rely on(44). By ensuring that the experts give their opinion on a common set of agreed or assumed facts, a situation where parties provide their experts with separate sets of instructions and facts, skewed in their respective favour, is avoided.
34. The impact of these changes as a solution to the concerns I articulated at the start of my address is obvious. By making the court the primary gatekeeper, expert evidence will only be adduced in necessary cases. By requiring the parties to agree as far as possible on a common expert, the problems of partisanship, obfuscation of issues, costs and delays are effectively addressed. Even where the parties cannot agree on a common expert, they are still required to agree on a common set of issues and facts which facilitates the evidence-taking process immensely. Where necessary, the court can also direct expert conferencing and “hot-tubbing” to facilitate the presentation of expert evidence. All in all, the new Rules represents a much-needed response to the concerns on the use of expert evidence, and a return to fundamentals.
35. I conclude by returning to the question I had posed earlier: is the adversarial approach the best way to harness the benefit of expert evidence in civil litigation? While expert evidence is undoubtedly indispensable, if necessary, it is obvious that the adversarial process has struggled to manage the challenges that its deployment has posed. In some cases, issues of bias and partisanship have undermined the credibility of the experts, and in turn, the utility of their evidence. In others, conflicting expert opinions have presented intractable differences that simply do not help the dispute resolution process.
36. The new Rules marks a welcome transformation to modernise the process by shifting away from the adversarial model and empowering the court to regulate the use of expert evidence. The new Rules mitigates the problem of bias and partisanship. At the same time, it reduces the costs and delays associated with the use of expert evidence, and in the process, levels the playing field for financially less capable parties. This evolution marks a paradigm shift in our approach and more importantly, makes justice more accessible to all.
I wish everyone a successful symposium. Thank you very much.