It is an ancient common law rule that on a subject requiring special knowledge and competence, evidence is admissible from witnesses who have acquired the necessary expertise on that matter, and such witnesses are known as "experts".  The foundation of the use of expert witness in court was laid down by Lord Mansfield in Folkes v. Chadd  that "the opinion of scientific men upon proven facts may be given within their own science." Although opinion evidence is inadmissible as a general rule, the main exception to this rule is the opinion of an expert on matters resting within his expertise, and this exception applies in both civil and criminal cases. Regarding the civil proceedings, the statutory recognition of the exception is reflected by section 58(1) of the Evidence Ordinance (Cap 8) that an expert's opinion is admissible "on any relevant matter on which he is qualified to give expert evidence". However, there is an issue of potential conflict of interest on the expert witness.  On one hand, an expert witness has a paramount duty to assist the court; on the other hand, he is remunerated for his services by one of the parties under the adversary system, which assumed a "more partisan role" for them at the expense of impartiality. 
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This essay aims to examine whether the aspiration of expert objectivity is realistic in our adversary system. In the next part, we shall discuss the problem of adversarial bias as well as the duties of expert witnesses. In part 3, the applicability of court appointed experts in Hong Kong will be examined with reference to the inquisitorial system. In part 4, we will explore the problems associated with the small population of potential experts in Hong Kong, followed by the court's power in dealing with expert disagreements in part 5. Finally, a conclusion will be drawn in the last part of this paper.
The problems associated with expert witness
It is often said that the principal danger of adversary expertise is "motivational bias".  As expert witnesses are employed by one of the parties to the litigation and they would purposely mould their views to fit their client's proceedings. In fact, the problem of lack of objectivity in expert evidence is not a new phenomenon. As early as in Lord Abinger v. Ashton  , Sir George Jessel said: "Undoubtedly there is a natural bias to do something serviceable for those who employ you and adequately remunerate you," and expert witness may even considered themselves as the "paid agents" of their employers. The problem of adversarial bias is also "widespread" in Hong Kong.  As identified in the Interim Report of the Working Party on Civil Justice Reform, a major problem concerning expert evidence is the partisanship and lack of independence among experts.  Thus, it is suggested by Professor Gary Edmond that partisanship may be "an unavoidable feature of knowledge production and expert opinion". 
Another reason for lack of objective expert evidence is due to the problem of "expert shopping", which is a process of selecting opinions from one expert after another, until the most favourable opinion to the party's case is found.  Since the choice of experts lies with the parties, the expert evidence is selected on the basis that would serve the best interests of their client's cases. Consequently the court does not necessarily obtain the most independent or objective expert evidence. The practice of selecting the "most favorable expert" is indeed a distortion of the rationale behind expert evidence as well as a discredit to the administration of justice.
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2.1 The duties of expert witness
Due to the concern about the failure of experts to provide an independent and objective opinion, a developed code of conduct has been set out in National Justice Compania Naviera SA v. Prudential Assurance Co. Ltd. (The Ikarian Reefer)  to clarify the duties of an expert witness. The most important parts are the first two numbered paragraphs, which stated that: "1) Expert evidence presented to the Court should 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  ." The Ikarian Reefer guidelines remain a good law in Hong Kong, and the relevant principles were set out in paragraph L1/58/7 of Hong Kong Civil Procedure 2009. The expert witness's "overriding duty" to provide independent and unbiased assistance to court is also reflected in Order 38, rule 35A of the Rules of the High Court (RHC) as well as the Code of Conduct for Expert Witness in Appendix D of RHC. Further guidance is provided in Hong Kong Air Cargo Terminals Ltd. v. Commissioner of Rating and Valuation  that an expert also needs to ensure no omission of material facts that could divert from his concluded opinion.
Although the adversary system may not have provided an ideal environment for the expert witnesses to maintain their independence and objectivity from their clients, I believed that the promulgation of code of conduct would have raised awareness of the expert witnesses in meeting the court's expectations, so that they will be less easily manipulated by lawyers, which can tend to rein in the "widespread" problem of expert bias in Hong Kong.
Apart from a code of conduct for expert witnesses, some commentators have recommended other ways to reduce the problem of expert bias, and one of them is the appointment of court experts with reference to the inquisitorial system. It is common for the court to appoint experts in many continental jurisdictions, such as Belgium, Germany and France. Unlike the way to appoint experts under the adversarial system, the expert witnesses are selected and remunerated by an independent authority, usually the court rather than the parties, which may avoid the problem of adversarial bias.  Take an example of the French system of expertise, the judge would normally commission the expert witnesses from a list of official experts, and they will be questioned by the judge.  The major distinction between the adversarial and inquisitorial system of justice is that the parties play a minimal role in locating evidence and they need not actively engage with the expert witness in court, as the expert witness is infrequently cross-examined by the defendants. As the court-appointed expert has little interaction with the parties, they are more likely to give an objective and unbiased opinion to the Court.
Nevertheless, it is argued that the appointment of court experts under the inquisitorial system is contrary to the principles of the adversarial system of justice. Apart from the loss of right for parties to select their own expert witnesses, there are a number of arguments that go against the inquisitorial court-appointed experts. First of all, the main problem is that the court may place "undue reliance" on the evidence provided by the court-appointed expert, which may lead to an ultimate result that it would be the court-appointed expert instead of the judge who decides the case.  This is also highlighted by Lord Denning in In re Saxton that the appointment of a court expert in England is a "rare thing", as "the litigants realize that the court would attach great weight to the report of a court expert, and are reluctant to leave the decision of the case so much in his hands." 
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Second, it is difficult to ensure the validity or test the applicability of the expert evidence in inquisitorial systems due to lack of cross-examination and involvement of more expert opinion, which are fundamental features of the adversarial system. In the absence of challenges to expert evidence, its quality and reliability is therefore doubtful as there is no way to test the correctness of the expert conclusion.  Moreover, the exercise of court's power to appoint an expert is rare under Order 40 of RHC in Hong Kong. It is indicated in the case of Nguyen Ho & Others v. Director of Immigration  that the Court of Appeal has declined an invitation to appoint a court expert.
Consequently, the inquisitorial court-appointed expert is difficult to integrate in our adversarial system, especially the important feature of cross-examination which encourages critical scrutiny of the expert evidence is lacking under the inquisitorial system.  It is also of my view that the adversarial expertise may benefit the fact-finder in another way by providing a range of perspectives or interpretations that allows verification of the validity and accuracy of the expert evidence in Court.
Problems with small population of potential experts
As Hong Kong is confronted with the problem of parties obtaining "hired gun" experts,  the concern of expert bias may also arise when the "employer" of the expert witness is the prosecution. This is particularly the case for criminal prosecutions, where the expert witnesses are commonly and closely connected with the police or prosecution authorities. In fact, the small population of available experts in Hong Kong would render the reliance on expert witnesses "employed" by the prosecution inevitable, for instance, police officers may be called by the prosecution as witnesses to give evidence in drug cases regarding the average dosage of drug addictsâ€¦etc. One may nonetheless argue that relying on the prosecution's own officers as expert witnesses to provide opinion evidence would prima facie cast a doubt on their independence and objectivity in that case. Thus, it raises the problem of whether it is possible to restrict the officers of the prosecution from giving opinion evidence as an expert in his field to support the prosecution's case.
In R v. Chung Chen Hsin  (Chung), a police officer ballistics expert, who was possibly connected with the investigation, was called by the prosecution as witness to testify for them that the unusual weapon found in the defendant's hand luggage was a "firearm". The court has made some important points regarding the right of the prosecution authority to call its own officers as expert witnesses to offer opinion evidence. It is held that there is no requirement in a criminal proceeding where the expert witness ought to be independent of the prosecution authority, but a witness who is "competent and properly qualified" to provide his expertise would suffice.  Judge Stuart Moore also challenged the judgment in R v. Kai Tai Construction Engineering Company Ltd.  by claiming that "it was not a "material irregularity" for the prosecution to have called a properly qualified expert from the same department responsible for that prosecution," and there must be "powerful reasons" to cast a doubt on the expert called by the prosecution in order to justify the refusal to allow the prosecution's own officers as expert witnesses.  Moreover, even the expert witness is so closely connected to the case that he may be biased in favour of the prosecution, it is ultimately a matter remained for the jury to assess the weight to be attached to his testimony and the question of admissibility is irrelevant.
The rationale in Chung was reaffirmed in many recent cases, such as Tang Ping Choi & Another v. Secretary for Transport  , where the court held that an expert's evidence was not inadmissible merely due to the fact that he or she was an employee of one of the parties to the case. With limited human resources in Hong Kong, the fact that many expert witnesses have been employed by the party calling them is nearly inevitable, especially for the technical matters that require highly specialized experts to offer their opinion evidence.
Despite the possible lack of independence of the expert witnesses employed by the prosecution, it has been made clear by the Hong Kong courts that the expert evidence would not be excluded merely on that basis. Even though the expert witness may have produced a biased opinion due to his or her vested interest in the outcome of the case, it is only relevant to the weight to be attached to that expert's testimony rather than the admissibility of evidence.
With one of more expert witnesses giving opinion evidence at court, it is possible to have a clash of opinion between opposing experts. In fact, we may divide the discussion into two parts: one is the role the judge if this situation happens at the trial; while the other is the judge's powers to limit the extent of expert disagreement before the trial.
First of all, if there are conflicting expert's opinions during the trial, the judge will need to direct the jury correctly. It is held by the Court of Appeal in Plait  that the judge should not direct the jury in a way that it is a case of choosing between their opinion evidence. Rather, the jury should consider if there is a reasonable possibility that either the opinion of the prosecution or defence expert, when taken in conjunction with all the other evidence, is correct; then the jury should proceed on that basis.
For the second part, the introduction of Civil Justice Reform in Hong Kong has offered the courts more control over the expert evidence, including measures to reduce the expert disagreement before the trial. The most common way for the court to narrow expert disagreement is to direct an expert meeting and joint report  , where the experts of both sides will meet before the trial and indicate clearly in the joint report the reason for their disagreement with each other. The direction is supported by Justice Wood that experts moderate their opposing views in the expert meeting, or even reach agreement on the controversial aspects of their expertise.  It is also noticed that the experts have a duty to attend this pre-trial meeting and conclude with a proper joint report, or otherwise, the defaulting expert would have breached paragraph 12 of the Code of Conduct for Expert Witness. Furthermore, the court has an option to order the appointment of a "single joint expert" under Order 38, rule 4A of RHC. Under this scheme, parties may jointly choose the "single joint expert", or the court can select from a list prepared by the parties or any manner as the court may direct. Although the use of single joint expert may allow the fact-finder to have a simpler and less-biased picture over the technical matter, it is stressed in the Woolf's final report that the appointment of a single joint expert is mainly used to deal with the problem of "excessive and inappropriate use of experts" instead of bridging the differences of opinion between experts. 
As a result, it is believed that the direction of pre-trial expert meeting and joint report will be more useful to narrow the conflicting opinion between experts rather than the appointment of a single joint expert.
With increasing technological sophistication of issues in courts, it is no doubt that the expert witness is playing a more significant role in the judicial process. Unlike other witnesses, the expert witness has an overriding duty to the court to provide objective and unbiased opinion evidence. An absence of independence and objectivity on the part of the expert witness would be prejudicial to the court, and consequently lead to a devaluing role of the expert witness in the court proceedings. It is opined that the introduction of the code of conduct as well as the new rules under the Civil Justice Reform in Hong Kong have evolved new roles for the expert witness. By setting court expectations in respect of the expert evidence, the expert witness would strive to meet the high standards and adhere to their duties and responsibilities listed in the rules.
Despite the effort of the expert witness, I believe the concerted efforts by all streams of the judicial system are also vital to restore not only the credibility of the role of expert witness, but also public's confidence in the administration of justice.
M. R. Damaska, 'Evidence Law Adrift' (New Haven & London: Yale University Press, 1997)
Mike Redmayne, 'Expert Evidence and Criminal Justice' (OUP, Oxford 2001)
Peter Murphy, 'Murphy on Evidence' (10th edn OUP, Oxford 2008)
Simon NM Young, 'Hong Kong Evidence Casebook' (Sweet & Maxwell Asia, Hong Kong 2004)
ARTICLES & REPORTS
Charles Pugh & Marcus Pilgerstorfer, 'Expert Evidence: The Requirement of Independence' (2008) Journal of Personal Injury Law 224.
Chief Justice's Working Party on Civil Justice Reform, 'Civil Justice Reform: Interim Report and Consultative Paper' (2001)
Gary Edmond, 'After Objectivity: Expert Evidence and Procedural Reform' 25 Sydney Law Review 131.
Gary Edmond, 'Judicial Representations of Scientific Evidence' (2000) 63 Modern Law Review 216.
J.R Spencer, 'Court Experts and Expert Witnesses: Have We a Lesson to Learn from the French?" (1992) 45 Current Legal Problems 213.
Lord Woolf MR, 'Access to Justice: Final Report to the Lord Chancellor on the Civil Justice System in England and Wales (HMSO, London 1996)
Peter Alldridge, 'Forensic Science and Expert Evidence' (1994) 21 Journal of Law and Society 136.
Samuel Gross, 'Expert Evidence' (1991) Wisconsin Law Review 1113.
Cliff Buddle, 'Judge calls expert witness mercenary' SCMP (22 March 2002) EDT 7.
Justice Sperling, 'Expert Evidence: The Problem of Bias and Other Things' (1999): <http://www.lawlink.nsw.gov.au/lawlink/supreme_court/ll_sc.nsf/pages/SCO_speech_sperling_030999> accessed 13 March 2011.
Justice Garry Downes AM, 'Expert Evidence: The Value of Single or Court-Appointed Experts' (2005): <http://www.aat.gov.au/SpeechesPapersAndResearch/SpeechesAndPapers/Downes/pdf/ExpertEvidenceNovember2005.pdf> accessed 13 March 2011.
Michael Wilkinson, 'Recent Developments Affecting Expert Evidence' in Law Lectures for Practitioners (1991): <http://sunzi.lib.hku.hk/hkjo/article.jsp?book=14&issue=140013> accessed 13 March 2011.
Folkes v. Chadd  99 ER 589
Hong Kong Air Cargo Terminals Ltd. v. Commissioner of Rating and Valuation  2 HKLRD 702
In re Saxton  1 WLR 968
Lord Abinger v. Ashton  22 WR 582
National Justice Compania Naviera SA v. Prudential Assurance Co. Ltd.  2 Lloyd's Rep. 68
Nguyen Ho & Others v. Director of Immigration  Civ App No 135 of 1990
Plait  CrimLR 332
Polivitte Ltd. V. Commercial Union Assurance  1 Lloyd's Rep. 379
R v. Chung Chen Hsin  1 HKCLR 120
R v. Kai Tai Construction Engineering Company Ltd.  2 HKCLR 26
Tang Ping Choi & Another v. Secretary for Transport  2 HKLRD 284
Whitehouse v. Jordan  1 WLR 246