Expert witnesses have been under fire recently. Their role in some high profile cases has attracted public disquiet, and sometimes ill-informed criticism in the press, as well as draconian professional discipline. It is very important not to allow the experts upon whom the delivery of justice in our courts so often vitally depends to become frightened or deterred, as anecdotal evidence suggests is beginning to happen.

An expert qualified by learning and experience may give evidence of his opinion in court, as an exception to the otherwise general rule that a witness may only give evidence of fact. The rationale for this is not that the expert’s opinion will be definitive of guilt or innocence, or in a civil case determinative of the outcome of the dispute. It is rather that in trials which involve complex issues of which the Judge and/or jury are ignorant, they should be helped to understand those issues by specialists who are able to explain and to interpret them.

Plainly it is not, nor should it be, any offence on the part of such an expert that in the view of judge or jury his opinion is ultimately not persuasive, or that it is held to be mistaken or wrong, or is for whatever reason disregarded or not preferred. Provided his opinion is honestly held, and impartially presented after careful enquiry and research, the expert witness has done his duty, and done it properly. Just as a barrister is not negligent for the fact alone that his advice turns out to have been mistaken, nor a doctor simply because his treatment fails to work, so an expert witness who has diligently formed an opinion, and honestly expressed it, is not guilty of impropriety, and cannot be professionally culpable for the fact alone that his opinion is not accepted at trial, or is held after forensic enquiry to have been wrong.

By way of example, there will in every contested medical negligence action be two opposing and often diametrically contrary opinions expressed by experts on either side. Those opinions may be presented, entirely fairly and honestly, in terms which allow no middle ground whereby each represents part of the truth. Unlike the situation at a scientific symposium, where the audience may take away their impressions of the differing views for further thought or research, and one day reach a scientifically conclusive view on way or the other, the expert witnesses’ opinions are offered in the context of an adversarial trial, a process designed to arrive there and then at an answer which favours one side of an argument over the other.

In this civil context the judge must decide which of the two should prevail, always of course with the unscientific luxury of determining the issue “on the balance of probabilities”. In effect he will be deciding that one of them is most probably wrong, or at least not provenly right, about the significance of the facts, and/or about the justification for the decisions or actions of the defendant. Yet at the end of these cases we do not expect a hue and cry, or allegations that the expert whose opinion has been rejected has acted dishonestly, improperly or culpably. Particularly in medicine, but also in other specialist disciplines, there is often room for opposing views to be held by experts whose respective interpretations of the facts, or of the inferences properly to be drawn from the facts, differ markedly on grounds which are at least arguable, and are advanced with complete sincerity.

To say this is not to excuse some of the more extreme errors of which unwise experts can be guilty. To use lurid or simplistic language in conveying an opinion to a judge or jury is never justifiable, though there may be a very fine line between translating abstruse scientific concepts into language which lay audiences can understand, as the expert has to do, and over-dramatising or dumbing down the material which it his task to get across.

Sir Roy Meadow gave evidence in the Sally Clarke trial of a kind and in a manner which led, subject to his pending appeal, to a finding of Serious Professional Misconduct and erasure by the GMC. It appears not only that his excursion into erroneous statistics about the chances of two cot-deaths in one family probably had little if any impact on the outcome of the trial, but also that the statistics themselves were derived from published material which might have been thought to be irreproachable. Nevertheless it is an essential part of the job of lawyers who call expert evidence to satisfy themselves by rigorous enquiry of the weight and the validity of the relevant expert opinion, and to subject it to logical analysis, before they lead it from the witness box.

Statistics is a science well known to be arcane, if not impenetrable. I speak with hindsight, but the concept that a cot-death might be genetically predetermined would at least suggest as a possibility that another in the same family might be more, not less, likely than normal. Again in hindsight, but as an important illustration of the principle, it would have served the prosecution team well to have enlisted a professional statistician to verify the apparently compelling statistical contentions to be advanced by a witness whose special field was paediatrics. Just as importantly it ought to have been a crucial part of the defence role to have challenged what Sir Roy proceeded to say in court, of which they will have had advance notice in the form of his witness statement. It does not appear to me that they did so, or that they marshalled or advanced a reasoned case against it, with or without the assistance of a professional statistician.

So my message is that in any court proceedings involving expert evidence, barristers and solicitors need to be keenly aware of the necessity to establish, to their own satisfaction and to a high standard, the strength of expert opinion on which they wish to rely, and how well it withstands the case made against it. This requires detailed exploration at the outset with the expert’s assistance, and putting it robustly to the test of contrary views which subsequently emerge in reports from experts on the other side.

If this task is properly carried out it will serve as a solid protection for expert witnesses against accusations of bias, or of impropriety, and of course in the end of professional misconduct. If and insofar as the expert has, unwittingly or otherwise, gone out unreasonably on a limb, he will be reminded of that before his report is exchanged or the trial begins. If he has strayed outside his field, that will become apparent and the pitfalls and the criticisms avoided. To the extent that his opinion is weakened or even undermined by cogent expert opinion on the other side, he will have been enabled, and will no doubt be glad, to confront and recognize this, and on reflection to rethink and, if necessary, to revise and/or recast the advice he is giving. For there are few less edifying experiences than that of an expert who comes belatedly, after the trial has begun, to the realization that the opinion he has given, and on which the lawyers have been proceeding all along, is erroneous, or substantially less supportable than he had hitherto believed it to be, and that he can no longer advance it with conviction before the judge or jury.

If matters are conducted in this way, it will be rarely if ever that an expert presents to the court an opinion or argument that is so unreasonable or unsupportable that his bona fides are called into question, or his professional conduct impugned. Opinions which are excessively partisan, or overly dogmatic, or undermined by cogent and compelling evidence from the other side, or are otherwise incapable of withstanding logical analysis will be exposed before trial begins, and reliance upon them avoided. What is more, if lawyers do their duty in this way a further huge benefit will be gained. I speak of the avoidance of the crushing blow to the party whose unjustified claim collapses, or whose unsustainable defence is dismantled only after the matter has been taken to a trial upon which so many hopes have rested for so long.

That is the right way to avoid the kind of problems which beset Sir Roy Meadow, and which have sent a shiver down the spines of many experts, no matter how conscientious they may be. It will provide the best possible protection for the expert against allegations of misconduct, for the parties against potential injustice, and for the courts against the presentation of evidence which is later alleged to have tainted or undermined the trial process.