Expert witnesses: The importance of independence and impartiality
The Court of Appeal recently found that a trial judge would have been entitled to exclude the evidence of an expert witness whose independence was challenged in cross-examination.
The claimant was a district judge who in 1999 underwent an MRI scan of the brain after an episode of visual disturbance. Dr Barker, a consultant neuroradiologist, reviewed the scan and reported that it was entirely normal. In 2011, the claimant had an aneurysm and suffered partial blindness and paralysis.
The trial judge found that Dr Barker (the defendant) had negligently failed to identify an aneurysm in the course of his review in 1999.
The expert witness
The defence relied on the expert evidence of Dr Molyneux, a consultant neuroradiologist with a distinguished clinical career. However, the trial judge came to doubt his impartiality and objectivity. The trial judge admitted the evidence but warned that the weight of the evidence was significantly diminished.
Lack of professional objectivity
In advance of the trial, Dr Molyneux did not report having any connection to Dr Barker. However, during cross-examination, it transpired that the relationship between the practitioners was “lengthy and extensive”. It became apparent that Dr Molyneux had:
- trained Dr Barker during his seven years of specialist radiology training;
- helped Dr Barker become a consultant;
- co-authored at least one publication with Dr Barker; and
- held office with Dr Barker at the British Society of Radiologists.
Dr Barker admitted that Dr Molyneux had guided and inspired his practice and that he suggested Dr Molyneux as a defence expert. Dr Molyneux, in an “unguarded moment”, referred to Dr Barker by his first name “Simon”.
The trial judge found that Dr Molyneux was not presenting himself as an expert having the necessary professional objectivity or emotional distance from the defendant. Therefore, the weight of his evidence was significantly diminished.
The issue of non-disclosure
The trial judge also found a substantial failure by Dr Molyneux to disclose the nature and extent of his connection to Dr Baker. The expert witnesses were specifically directed to raise any potential conflicts of interest in their reports. However, the trial judge found that Mr Molyneux “did nothing”. Dr Molyneux’s curriculum vitae also omitted publications which he and Dr Barker had co-authored. The circumstances raised “a natural suspicion that the default was not inadvertent”.
The Court of Appeal’s decision
Dr Barker appealed the decision. The Court of Appeal not only affirmed the trial judge’s decision but stated that he would have been justified in excluding the evidence all together.
Success or failure in a case can depend entirely on the judge’s assessment of the expert evidence. Therefore, litigants should not give the court any reason to doubt the independence or impartiality of their expert witness.
The litigant must carefully assess whether they have any kind of relationship with their expert witness which could give rise to a conflict of interest. Where a conflict exists, it does not necessarily mean that the evidence will be excluded but it may diminish the weight of the evidence. Much depends on fact and degree. It is not enough that the expert witness is distinguished in their field. They will have to demonstrate that they:
- know that their primary duty is to the court; and
- are willing and able to carry out that duty notwithstanding any connection to the litigant.
The litigant and the expert witness must also give full and honest disclosure of any potential conflict from the outset of the trial. Where disclosure is not made and a conflict of interest later emerges in evidence, the judge will have good cause to doubt the ability of the expert to fulfil their duty to the court.