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Impartiality of Expert Witness: Defining and Measuring this Construct

Special Reports

by Hugh Koch & Paul Elson, Chartered Psychologists Hugh Koch Associates, Cheltenham,UK

Physical and psychological evidence in civil case claims impacts significantly on legal discussions (1). To obtain this evidence, the court relies on medico-legal expert witnesses to be impartial, independent and fair. But how can this construct ‘impartiality’ be defined and, once defined, how can it be operationalised and measured? Only then can the appropriate training and continuous professional development (CPD) be provided to ‘raise the bar’ of expert witnesses in this crucial area.

The duties of an expert witness are to help the court in matters within their expertise, overriding any perceived obligation or partiality to the instructing party and requires them to deal with cases proportionally, expeditiously and fairly (9). The Civil Procedure Rules (CPR; 1999) exhort experts, in the expert’s declaration as follows: “

“I have not included anything in this report which has been suggested to me by anyone, including the lawyers instructing me, without forming my own independent view of the matter.”

The word ‘impartiality’ is a broad concept and can denote different practices (2). It includes the following ideas:

1) Opinion free of bias or prejudice

2) Even handedness

3) Basing opinion on objective criteria

4) Absence of distortion of information presentation

5) Critical analysis with recognition of biases

6) Understanding the influences experienced

This is also referred to us in the European Union Law in the Charter of Fundamental Rights (of the EU) in the following reference: “Every person has the right to have his or her affairs handled impartially, and fairly by agencies of the Union”. (Article 41) (3).

Manifestation of Expert Witness Impartiality

Independence and impartiality in expert witness behaviour is seen in the following ways: -

Objectivity – the fair and equal treatment of claimants Operational Impartiality – assessment not linked to any other professional or business pricing factors

Objective Impartiality – assessment procedures must appear impartial to the claimant, defendant and others

Internal Impartiality – the various functions of the assessment must be coordinated logically (e.g. testing, behavioural analysis, mental state examination or physical examination)

There are several types of bias which can be evident:

a) Confirmation Bias – tendency to highlight supporting ideas rather than differing ideas

b) Belief Perseverance – stubborn insistence on a belief despite established contradictory evidence(s)

c) Overconfidence Bias – tendency to reach decision when some supporting evidence exists but not all evidence has been critically examined

Objectivity and Impartiality

Ways in which expert witnesses operationalise impartiality include:

1) Verifying information in several sources (i.e. not relying on just one or two sources of information)

2) Examining and evaluating information and its sources (identifying potential bias in what sources are selected/used)

3) Having procedures to deal with any conflicts of interest in providing an expert opinion

4) Being transparent about how assessment(s) are carried out and conclusions reached

Impartial and valid use of scientific evidence

Expert witnesses play a pivotal role in offering scientific evidence to the court (4). Lawyers tend to prefer forensic science over social and psychological science in criminal cases but it is not clear whether this occurs in civil cases. In all probability, due to a lack of understanding, lawyers are often unclear about the importance of social and psychological science and research relating to the court and provision of robust, impartial evidence. There is a continued need for the education of lawyers and court room personnel regarding the utility of social science in the legal system and how this helps to identify how prior beliefs and prejudices impact in court.

Relationship between Impartiality and Certainty

Expert Witnesses are encouraged to express certainty when describing their ‘expert opinion’ – historically this has taken the form of general pronouncement rather than empirical data analysis. Experts typically express this general certainty with phrases such as ‘on the balance of probabilities’ and ‘predominantly’ or ‘partially’. Experts have a long standing ambivalence about these terms when called upon to convey their level of confidence in their opinions (5).

The concept of Intolerance of Uncertainty (10) has recently been applied to expert psychologist witnesses (6) both in terms of its prospective (future-orientated) factor and behavioural (dealing with uncertainty) factor and how to manage and tolerate the emotional experience of uncertainty

Impartiality and the medico-legal trail

There are many pitfalls for the unwary expert (8) at different stages in the typical medico-legal trail.

Implications of Impartiality

An expert witness should recognise the utmost importance of impartiality and the potential conflicts of interest in promoting confidence and certainty about expert opinions. The highest standards of independence and impartiality should be applied to all assessment and reporting activities in accordance with best practice.

An expert should utilise and display a level of critical thinking that facilitates an objective analysis of facts from complex, various sources as follows: -

• The process of actively and conceptualising, applying, analysing, synthesizing, and evaluating information to reach a conclusion

• Disciplined thinking that is clear, rational, open-minded, and informed by evidence

• Reasonable, reflective thinking

• Purposeful, self-regulatory judgment which results in interpretation, analysis, evaluation, and inference, as well as explanation of the evidential, conceptual, methodological, or contextual considerations upon which that judgment is based

• Thinking about one’s thinking in a manner designed to organise and clarify, raise the efficiency of, and recognise errors and biases in one’s own thinking

The expert uses critical thinking to solve evidential problems – using critical thinking to improve the process of thinking (7).

Measuring Expert Impartiality

Current research is underway to measure levels of impartiality amongst expert witnesses. This will be subject of future publication. A prototype scale for this has been developed by the second author. 

Conflict of interest and objectivity behaviours should be covered through annual training or CPD sessions to ensure all assessment activities are conducted in an independent, and impartial manner.

From a cognitive/emotional view point, the ability to maintain a critical thinking impartiality requires the expert to use mindfulness and anxiety management to tolerate the uncertainty inherent in complex presentations, in the general context of good time and paper management. n

Training and CPD

Having formulated a logical understanding and definition of impartiality, a practical implication is the provision of training and development in perceptions, inclinations and behaviours to provide opinions in an impartial way and action ways, as an expert witness, which takes into account and corrects inherent biases.

Training in types of errors and biases inherent in expert work is important. Basic recognition of scientific validity and reliability including personal or self-serving biases would be beneficial.


1. Koch HCH (2016) Legal Mind: Contemporary Issues in Psychological Injury and Law. Expert Witness Publications. Manchester.

2. Stanford (2017) Impartiality. Stanford Encyclopaedia of Philosophy.

3. European Parliament, Council and Commission (2012) Charter of Fundamental Rights of the European Union. 26.10.12.

4. Wechsler HJ, Kehn A, Wise RA & Cramer RJ (2015) Attorney Beliefs Concerning Scientific Evidence & Expert Witness Credibility. Int. J. Law and Psychiatry 41,58-66.

5. Drogin EY, Commons MC, Gutheil TG, Meyer DJ and Norris DM (2012) ‘Certainty’ and Expert Mental Health Opinions in Legal Proceedings. Int. J. Law and Psychiatry. 35, 348-353.

6. Koch HCH, Carleton RN & Cosway R (2016) Managing Uncertainty in Experts: What are the key issues? Expert Witness Journal

7. Wikipedia (2017) Critical Thinking. www.wikipedia.org/wiki/critical_thinking

8. Koch HCH (2017) Impartiality of Medico-Legal Experts. Expert Witness Institute Newsletter. Spring.

Other bodies unrelated to the Civil Justice system have been consulted over impartiality. These include: The Ombudsman Association; Finnish Accreditation Service (FINNAS).

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