Legal control of expert witness bias
| Published date | 01 January 2017 |
| DOI | 10.1177/1365712716674798 |
| Date | 01 January 2017 |
| Subject Matter | Articles |
The International Journal of
Evidence & Proof
Legal control of expert
2017, Vol. 21(1-2) 69–78
ª The Author(s) 2016
witness bias
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DOI: 10.1177/1365712716674798
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Mingxiao Du
China University of Political Science and Law, Beijing, China
Abstract
Impartiality of expert witnesses means that such experts operate within scientific principles and
legal procedures. By doing so, they assist the trier of fact. There are two aspects to the
requirements for the impartiality of expert witnesses: the individual perspective and the
industry perspective. Each expert witness must follow individual standards, including avoiding
irrelevant information affecting his or her opinions; applying reliable methods; employing rea-
sonable analysis; and providing the findings in comprehensive reports (including a precise
description of personal background and expert activity). They must also follow industry stan-
dards of forensic science regarding objective technical accessible demands, laboratory man-
agement and career management. Biased expert witnesses, however, will damage impartiality
and impede the goal of assisting the trier of fact. Based on psychological theories such as dual
process theory, authoritarian personality and intergroup threat, this paper classifies expert
witness bias into four categories: (1) cognitive bias; (2) bias in the analytic process; (3) bias
resulting from the position of the expert witness at trial; and (4) the social bias arising from
social pressure or economic pressure. Because bias influences the relevance, credibility and
impartiality of experts, steps should be taken to restrict certain categories of bias, which can be
and must be controlled. Reflecting the differences between the Anglo-American legal system
and the Chinese legal system, in China the bias of expert witnesses should be controlled in
terms of actions, occupational management and independence of laboratories.
Keywords
expert witness bias, impartiality, legal control
Meanings of impartiality of experts
The authenticators and authentication institutions engaging in proving scientific facts must abide by the
laws and regulations, professional ethics, occupational disciplines, and technical operating standards (see
Wang and zhang, 2013: 9). This paper concerns the standards of impartiality for experts and argues that
Corresponding author:
Mingxiao Du, Institute of Evidence Law and Forensic Science, China University of Political Science and Law, 25 Xitucheng Rd,
Haidian, Beijing, China.
E-mail: dumingxiao@163.com
70
The International Journal of Evidence & Proof 21(1-2)
experts should base their opinions only on the materials submitted to them, using the analytic methods
and interpretive tools accepted by the peers in their field.
Some scholars argue that experts are expected to make their decisions as judges or juries, making
their opinions standing in the middle (see Hu, 2014: 194 and Zhang, 2003: 380). But experts are not the
triers of fact, because the information they rely on is usually provided by one side rather than by the two
parties. While the task of experts is helping judges and juries find the truth, they are not the ones making
the ultimate decisions. As a result, the experts cannot obtain all the materials because the experts are
hired by one party. Even in inquisitorial systems, in which experts are not sponsored by the parties but
instead by ‘the system’ (Malsch and Freckelton, 2009: 127) and therefore may obtain more all-around
information, they still give their opinions based on information they obtained.
Impartiality is the core of forensic science
One of the roles of experts is to evaluate scientific findings and the results of analytical tests in the
context of the relevant case circumstances. Because the forensic evidence is highly specialised, it is
difficult for judges and juries, who are usually lacking in scientific and technical knowledge or expe-
rience, to understand. If expert witnesses are unfair, it is difficult for the trier of fact to identify the bias
as well as to reach the truth.
The impartiality of expert witnesses requires that the expert should avoid the dispute between the two
parties, and instead give his or her testimony exclusively based on the materials. Their opinions need to
be evaluated by their peers directly and unambiguously.
To help the trier of fact discover the truth, experts must be impartial. Using scientific methods to
analyse scientific evidence will help the trier of fact resolve unsolved issue. Forensic science plays an
important role in solving key problems, such as such as helping the trier of fact to understand a fact in
issue or the evidence, which are the cores of the cases and special knowledges (see Zhu, 2006: 15). So
the answers are expected to be right, or at least should not be based on incorrect science. The expert
testimony may only be the part of truth, which is beneficial to the commissioning party, but cannot be
allowed to confuse the trier of fact. Because the judges, lawyers and both the sides may be the laymen,
all of them lack the ability to discover errors in the expert’s opinion or methodology.
The equality of procedure requests the impartiality of experts. The equality of process means that
both sides could hire the experts, helping them to find the truth based on the information they obtain.
From this point of view, the gap between the opinions given by experts of the sides is normal and
logical, because of the different information and materials they have and because of their adversarial
standpoints. During cross-examination, judges or jurists can find the truth after considering the experts
testimony of both sides, and evaluating which story is more credible depends on the decision of the trier
of fact.
Standards of impartiality of experts
This paper examines the requirements for the impartiality of expert witnesses from two perspectives, that
of perspective of individual experts and the industry perspective.
Requirements of perspectives of individuals
Each expert witness needs to follow the requirements for experts, including: avoiding irrelevant infor-
mation affecting his or her testimony; applying reliable methods; using reasonable analysis; and pro-
viding comprehensive statements.
Cumulative information includes irrelevant or extraneous information and tendentious informa-
tion. Extraneous information may confuse the experts, while tendentious information may lead to
wrong decisions.
Du
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Reliable methods are central to the impartiality of experts. The primary function of experts is to use
scientific knowledge, experience and technology that other people involved in the case are not familiar
with to help those people know vital facts. As a result, applying reliable methods is the first require-
ment of expert witness impartiality. Furthermore, information about the case is the premise of the
reliable methods.
Well-founded analysis is the bridge between the scientific conclusions and the truth. But it is hard to
devise a legal standard to determine whether the analyses made by the experts are well-founded. Experts,
who are proficient in their fields, help laymen to make decisions about the expert’s procedure, which
means that where the analysis is not reasonable, this is a fact that laymen could not perceive without
expert assistance. Because unjustified analyses may lead...
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