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Legal Mind Case and Commentary No 40: Expert Witnesses, Beware Unconscious Bias - [Koch HCH, Jansen F, Maisey D and Natha F, November, 2022]

08/11/22. This is the fortieth in a series of Case reports and Commentaries from Professor Koch and colleagues.

This month’s Legal Mind Case and Commentary summarises and comments on an excellent article by Meera Shah in Bond Solon newsletter and recent PLC Dispute Resolution blog. It relates to comments made by A. Meltzer QC in November 2021 about the inappropriate conduct of two experts and advises against forming opinions of a claimant suggesting a level of unconscious bias.

The Case:

In a 12-day trial concerning minor traumatic brain injury (RTA related), a claimant did not appear to suffer immediate significant head injury and returned to work relatively quickly. 3 years later her work was disrupted, and she displayed physical and neurological symptoms. Liability was admitted and the trial centred around causation and quantum. Defence comments about honesty and information omissions were made.

The judge rejected the relevance or validity of inconsistencies and did not make a finding of fundamental dishonesty. The judge criticised one expert for ‘judgemental’ comments and pejorative statements such as “self-pitying” and “histrionic” and excessive reliance on small, negative details indicative, in the Judge’s opinion, of unconscious bias. The judge also found evidence of partiality and insufficient adherence to CPR rules (Part 35).


The psychology of communication reflects on how our beliefs and attitudes can be inappropriately focused on insufficient information resulting in pejorative comments about others. This ‘unconscious bias’ was what Judge Meltzer was referring to in this case.

Whilst bias is a normal part of communication, it can often reinforce stereotypes. To combat this bias, it is important that experts and lawyers learn about different types of bias, how they might surface in a case, and how to avoid them.

These biases which encompass both positive, favourable and negative, unfavourable assessment are often involuntary, and not in an individuals’ intentional control. Three typical biases are:

1. Confirmation bias: - developing a view and only selecting further views which reinforce initial view.

2. Attribution bias: - making a quick judgment without having a full story e.g., a person being late.

3. Halo effect: - forming an opinion based on one positive or negative observation.

Unconscious bias can be avoided by taking great care to obtain multiple examples of a claimant’s behaviour and recall and observing one’s internal tendencies to jump to conclusions (often negative) about consistency, reliability and ultimately honesty.

It is crucial to observe one’s own use of language and to avoid pejorative descriptions such as those apparently used in this case (e.g., histrionic, self-pitying).

It is essential for expert witnesses to appreciate their CPR 35 duty to the court, to be impartial and balanced. Experts need to be well trained in this. Their opinions need to be objective and unbiased at all times and their tone of voice/language must not suggest any level of unconscious bias, and avoid placing unnecessary and questionable reliance on minor or irrelevant evidence.

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