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Year : 2017  |  Volume : 3  |  Issue : 2  |  Page : 82-84

The rational thinking of expert opinion and communicating in courtroom

Institute of Evidence Law and Forensic Science, University of Political Science and Law, Key Laboratory of Evidence Science, Ministry of Education; Collaborative Innovation Center of Judicial Civilization, Beijing, China

Date of Web Publication30-Jun-2017

Correspondence Address:
Bing Li
Fada Institute of Forensic Medicine and Science, No.26, Houtun South Road, Qinghe Xiaoying Area, Haidian District, Beijing
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jfsm.jfsm_52_17

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Since the past half century, expert testimony has played an increasingly important role in Chinese litigation. As the amount of expert testimony has grown, the issues about its admissibility and scientific foundation related to evidence are becoming to be questioned commonly. Since eighteenth central committee (China) adopted the decision of the Central Committee of China on several important issues in promoting the legal system, the evidence was redefined to become the predominance in the whole proceeding. This article reviews the expert knowledge implicit in the opinions. It argues that the expert opinions ask judges to be aware of the role of communicationg between participants. Expert opinion is not only gained from laboratory, but also socially constructed in the rational expression and communication, which requir us think logically in terms of legal perceptions of science and expert knowledge in the empirical world.

Keywords: Bayesian approach, conclusion scale, expert opinion, forensic evidence

How to cite this article:
Li B, Wang Y. The rational thinking of expert opinion and communicating in courtroom. J Forensic Sci Med 2017;3:82-4

How to cite this URL:
Li B, Wang Y. The rational thinking of expert opinion and communicating in courtroom. J Forensic Sci Med [serial online] 2017 [cited 2022 May 18];3:82-4. Available from: https://www.jfsmonline.com/text.asp?2017/3/2/82/209290

Eighteenth Central Committee (China) adopted the decision of the Central Committee of China on several important issues in promoting the legal system, in particular, prioritizing the importance of evidence in the evidence-judging doctrine. The decision made it clear that promoting trial as the center of the litigation system reform ensures that investigators and prosecutors can fulfill their responsibilities well, including but not limited to: understanding the importance of evidence, collecting and preserving the evidence, reviewing the evidence; encouraging witnesses and experts to the courtroom for the purpose of the trial in the fact findings so that the participants can testify the evidence, protecting litigation rights, and convicting fairly. It was pointed out that we should treat court-trial as the central part of the whole proceedings. In this process, the judge's use and scrutiny of evidence have increasingly important role. In the current situation, where science and technology are highly developed, evidence presented to the courtroom is more or less being influenced by the “expert opinions” or “forensic expertise.” However, for the “expert opinions based on impression identification,” such as signature and footwear mark, the arguments in robustness and reliability of those expressions of experts opinions are still under dispute.

For example, “expert opinion,” a subject of widespread concern in recent years, has been a hot topic among forensic scientists, jurists, legal practitioners, and other stakeholders in criminal proceedings. Since the issue was raised in 1990s, it has attracted more and more attention.[1] The debate on the subject presents an exaggerated trend after the report on “Strengthening Forensic Science in the United States: A Path Forward” was published by the National Academy of Science in 2009.[2] Based on it, the report produced a series of shock waves about the scientific debate of forensic science. Among them, the controversy about the scientific and reliability of the opinion of the forensic evidence has been a hot topic.[3] From the view of forensic scientists, effective and clear communication of the forensic findings and expert opinions (e.g., identification) in the courtroom are undoubtedly their most important task. Likewise, from the view of judges, lawyers and other participants, accurate and appropriate understanding of the expert opinion (forensic evidence) presented to them is very important. Therefore, the evaluation of expert opinion based on likelihood ratio is obviously more and more respected by forensic scientists. It is undeniable that the use of logic theory in the field of forensic science, to assist in evaluation of evidence in complex cases, should be a rational choice. However, from the current experience in western countries, the application of likelihood ration in expert opinion is somehow still in a free choice state and has not been promoted as an international standard.

Taking the opinion scale in China as an example, it is still under dispute among different groups [Figure 1], specifically, how should an expert present his/her opinion explicitly and be well accepted. Such discussions include how we construct the opinion scale? How many levels? Should we avoid presenting expert opinion with uncertainty? In general, as showed here, we applied this opinion scale to the conclusion part of forensic science report, according to the related guideline published by Ministry of Justice (China). However, we practically tend to decrease the frequency of using uncertain reporting terms to meet the preference of a judge, who looks forward to the categorical opinion. To make a generalization, in practice, identification, exclusion, and inconclusiveness are the three terms used much more frequently than the others.
Categories of expert opinions on impression identification

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Expert opinions, evidence, and probabilistic inferences are applied during these periods, including prelitigation, prosecution, and trial. Especially when it comes to forensic evidence (including several types of expert opinions) issued by forensic scientists, its role is particularly prominent.[4] More importantly, each participant in the proceedings is envisaged to be able to properly understand and process expert opinions (e.g., categorical opinions), the real meaning of the evidence and its logical relationship with the case itself. However, a large number of practical experience and recent statistical data show that serious misunderstanding or lack of understanding of expert opinions have a great impact on miscarriage of justice.

In practice, the form of forensic evidence is often questioned about the extent of its robustness and reliability due to the lack of uniform terminology, concepts or methods. Fundamentally, in court or the proceedings, expert witnesses (forensic experts) must meet the relevant competency requirements prescribed by the law before providing expertise. However, we must be clear that even if the expert witness is qualified in fingerprint, ballistic or psychiatry, it does not mean that he or she is also an expert in the field of statistics and probability. In other words, forensic scientists do not need to be a statistical expert, but holding a basic knowledge of statistics is necessary, to convey the probative value (relative weight of the evidence given a set of competitive propositions) of the evidence (findings detected by forensic scientists) to the court in a reasonable and fair way.[5]

Around the question of “forensic evidence,” reliable and effective communication among judges, lawyers and forensic scientists should be the sound approach to testify the evidence. However, “expert opinion with defects” or “expert opinion in question” might be caused by the factors such as the limitation of current science and technology, the lack of explaining the results of forensic examinations, the obstacles of understanding the expert opinion among forensic experts, lawyers and judges, and so on. The last point is usually a common case in judicial practice.

As we know, expert opinion is a sort of evidence that helps judge in fact finding. Accordingly, the primary task of expert is to communicate the observations or tested findings with participants in the court no matter by presenting in the courtroom or writing report. Then, you should make appropriate interpretation of your findings, such as given one proposition is that the signature was simulated from some known references and the other propositions were that it was genuine. After examination, you may find that there is apparent retrace along the ink lines between the questioned handwriting sample and reference one. Then, you also find an indentation on the reference sample at the same position as the questioned ink lines with the same shape. Then, what does it mean? You would say it is a simulation! I would like you to stay here for a while, giving you a few more scenarios: what if some other information was supplemented? For example, how about if the writer's hands were injured and his daily signature was usually signed on a pile of papers. In this case, what would you think? Clearly, you would reduce your confidence in simulation decision. What we mean in the case is that generally in real caseworks, experts cannot get enough relevant information. Therefore, we should be aware of the high risk of categorical conclusions.

The rational expression and logical evaluation of the expert opinion are obviously helpful for the progress of the proceedings. For example, lawyers need to have the related knowledge to be able to justify the use of statistical or probabilistic evidence, to find out the exposed flaws of this type of evidence.[5] However, for a judge, it is fundamental to be aware of the statistics or probabilities in court. Similarly, forensic experts need to have appropriate knowledge and experience to ensure that they can provide “genuine” expert opinion.

The 2nd Sino-Swiss International Symposium on Evidence Science advocates the promotion of a practical and informative assessment of the evaluation and interpretation of the guidelines,[1] namely, “ENFSI Guideline for Evaluative Reporting in Forensic Science-Strengthening the Evaluation of Forensic Results across Europe” (hereinafter referred to as “ENFSI guideline”). It includes not only the general background knowledge and basic principles that every judicial practitioner should be aware of but also covers the practice of forensic scientists to draw expertise in daily procedures of specific work, rules, as well as how different types of expert opinions can be more effectively and rationally expressed in court so that judges, lawyers, and the other legal participants can better understand the findings of forensic report. We hope that this modular guideline will meet the needs of practitioners such as judges, lawyers, and forensic experts. For instance, through the reference guideline, they can get relevant information to address the litigation process in the emergence of specialized issues.

The main content of ENFSI guideline is to provide a presentation framework that is more understandable to a legal practitioner (usually a layman who lacks forensic science knowledge) and that is consistent with a logical reasoning expression. The model is derived from the mainstream forensic science disciplines, supplemented by logical and probabilistic methods to solve the controversial issues involving specialized knowledge in the investigation, prosecution and trial phases. In addition, this logical model can also be applied to the analysis and interpretation of evaluative evidence at the stage of the proceedings. Emphasizing the validity of the expression of expert opinions is not only conducive to the parties involved in the trial stage in active communication among them to properly understand the meaning of evidence but it also helps to promote the forensic scientists more concerned about the improvement of tested methods, scientific knowledge, and so on.

The ENFSI guideline for evaluative report focuses on scientific evidence presented in court. The expert opinions will be more effectively and logically presented to judges and lawyers when they demonstrate the weight of evidence or evidential value through likelihood approach. The establishment of the model requires three stages; each stage has its own theme and core content, which can be regarded as the auxiliary tools of forensic scientists and judicial personnel in their specific caseworks.

To apply this logical model, we should first try to solve the problem of multiple professional audiences. It is more meaningful to have a court debate on this relatively equal level only if there is a common basis of the knowledge, skills and empirical reasoning for the judge, lawyer, forensic scientist and other participants. In this context, all the legal participants will be able to better understand opinions, questions, and doubts of the other participants. For example, lawyers may try to refute the flaws in the thinking process of probabilistic and statistical reasoning by directing the forensic scientists. As for the forensic scientists, possibly through attorneys' questions and their expectations for the expert opinion, especially relates to the probability, to exercise their “expert” ability to appear in court skills, and more proficient in the process of going through the various conditions.

Relying on the promotion and practice of the ENFSI guideline, combined with the specific practices of our domestic judicial practice, we need to think much about how we provide a coherent framework of knowledge and related practical programs to promote in specific caseworks. For example, which type of decision-making should be inferred based on the specific situation of the real case. Moreover, it should also play a leading role in reporting of forensic expertise and how forensic findings can be expressed effectively and appropriately. Bearing on this, it might be better way to begin by training the judicial practitioners including judges, lawyers, experts, and so on, about the foundational knowledge of probability and statistics in forensic evidence, or more specifically in expert opinions. This approach will also play a positive role in supporting judicial justice.

To sum up, science is a probabilistic cause and scientists should speak the language of statistics. The main solution for those issues of expert opinions presented in courtroom is to think about the rational expression of these opinions and logical evaluation and interpretation in court, as well as to encourage judicial practitioners to be aware of forensic evidence so that the parties in court understand each other equally and accurately.[6]


This research was funded by Beijing Law Society through Municipal law research project (2016), Grant No. BLS (2016) C005.

Financial support and sponsorship

This research was funded by Beijing Law Society through Municipal law research project (2016), Grant No. BLS (2016) C005.

Conflicts of interest

There are no conflicts of interest.

  References Top

Giannelli Paul C. The 2009 NAS forensic science report: A literature review. Crim Law Bull 2012;48:378-93.  Back to cited text no. 1
Committee on Identifying the Needs of the Forensic Science Community, National Research Council. Strengthening Forensic Science in the United States–A Path Forward; 2009.  Back to cited text no. 2
Sanders J, Diamond SS, Vidmar N. Legal perceptions of science and expert knowledge-admissibility standards: From frye to kumho tire. Psychology Public Policy and Law 2002;8:139-53.  Back to cited text no. 3
Simmross U. Appraisal of scientific evidence in criminal justice systems: On winds of change and coexisting formats. Law Probab Risk 2014;13:105-15.  Back to cited text no. 4
Roberts P, Aitken C. The Logic of Forensic Proof: Inferential Reasoning in Criminal Evidence and Forensic Science. Royal Statistical Society; 2014. Available from: http://www.rss.org.uk.  Back to cited text no. 5
Imwinkelried EJ. Should the courts incorporate a best evidence rule 7. European Network of European Network of Forensic Science Institutes. Strengthening the Evaluation of Forensic Strengthening the Evaluation of Forensic Results across Europe (STEOFRAE). into the standard determining the admissibility of scientifi c testimony: Enough is enough even when it is not the best. Case West Reserve Law Rev 1999;50:19-51.  Back to cited text no. 6


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