Medical statistical expert evidence refused

Related Sector: Expert Witness, Witness Familiarisation

On 16th June 2020, an application to rely on expert evidence from a medical statistician on the issue of life expectancy was refused by the High Court.

In Chaplin v Pistol & Allianz Plc [2020] EWHC 1543 QB, Mr. Justice Jay concluded that the expert evidence was not “reasonably required to resolve the proceedings”, for the purposes of CPR 35.1.

In making his ruling, he endorsed previous decisions on the use of life expectancy evidence that it should only be used in the following circumstances:

(i) where the relevant clinical experts cannot offer an opinion at all; or
(ii) state that they require specific input from a life expectancy expert; or
(iii) where they deploy, or wish to deploy statistical material, but disagree on the correct approach to it.

More broadly, medical statistical evidence is admissible but it is usually the starting point for medical witnesses to reach their clinical judgements. In other words, the medical experts refer to, interpret and rely on, the available statistical evidence in order to help them to arrive at their clinical opinions.

The statistical material would have to be seen as reliable and so, typically, it would need to be already published and peer reviewed.

In Chaplin, the two neurological experts had expressed reasoned opinions on life expectancy; neither had stated that they were unable to reach an opinion or that they needed additional expert input from a medical statistician.

There was a difference of opinion between them in the ranges that each gave; that difference had narrowed as a result of their discussion and was reflected in their joint statement.

The judge accepted that the main reason for the difference between them was a matter of clinical judgement, rather than statistical interpretation; to the extent that it was the latter, he took the view that both experts would be able to explain their interpretation so that the court could decide between their two approaches. They did not need “formal evidence from a statistician” to help them do so.

The courts take a pragmatic view of statistical evidence, allowing the medical experts to use published, peer reviewed data and explain it where necessary. Evidence from a medical statistician will only be allowed in the rare circumstances where the medical experts are unable to reach their own conclusions.

So where does this leave the clinical expert witness, who wants to refer to statistical evidence?

The courts’ approach is to allow the clinical expert to continue to use relevant statistical material, provided the data is reliable and provided that the expert stays within their expertise – in other words, they express their clinical opinion and do not stray into giving opinions on any statistical issues.

Author: Nick Deal, Barrister & Head of Expert Witness Training, Bond Solon
This article was first published on 25th June 2020