Supreme Court judge warns of ‘real danger’ of over-reliance by judges and juries on expert evidence

There is a “real danger” of judges and juries becoming so reliant on expert evidence that experts almost become the “deciders” in cases, a Supreme Court judge has warned.

This danger to the process of judicial decision may readily be avoided through the application of the rules constricting and limiting admissibility of expert testimony “but more readily by a proper mindset on the bench”, Mr Justice Peter Charleton said.

He said experts “are not to be afforded a celebrity status but are to be assessed from a distance” and that “no court should surrender to any expert”.

The warning is set out in an article The Safe Use of Expert Evidence, co-authored by the judge with Ivan Rakhmanin, a judicial assistant to the Supreme Court, and published in the latest edition of the Irish Judicial Studies Journal.

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Experts, the authors say, are privileged witnesses who can express opinions and may comment on the ultimate issue before the court, “territory beyond the reach of any other testimony”. They can provide invaluable, sometimes “indispensable”, evidence and, without the explanation of science, some cases, such as those involving issues of forensic pathology and psychiatry, would be “impossible” to try.

Adhering to the rules here governing expert evidence means such witnesses are a “rarity”, although personal injury lawyers have “almost by default” enabled trials involving experts “in even the most mundane of fact issues”, they wrote. This may be questioned “as may the judicial discipline that apparently enables that practice”.

They support the rule that experts may only be called in Irish courts to offer testimony on an “arcane” discipline, an area of fact outside general experience and outside the scope of knowledge and expertise of the finder of fact, whether judge or jury, such as the analysis of handwriting.

Expert evidence may be “ruinously expensive” and, without a clear rule concerning the numbers and use of experts, the principal of equality of treatments risks being unbalanced in favour of those litigants “with the deepest pockets”, they warn.

[ ‘Hired gun syndrome’ a risk with expert witnesses, judges warn ]

[ Experts are ‘independent’ in personal injury cases, solicitor says after judge criticism ]

One expert on each side is now the general rule here. While a single joint expert may be appointed once there is agreement of the parties involved, the report of the civil justice reform group has suggested Irish judges should have power to appoint a joint expert, as is the situation in England and Wales.

Such an expert, the article cautions, is likely to have “even greater sway” with the court than in a contest between experts nominated by the parties.

Criminal cases involving psychiatric evidence are a “truly difficult” area exemplifying the pitfalls awaiting a judge when it comes to expert evidence, the article states. A jury is not bound by psychiatric evidence, even when that is unchallenged, and the Supreme Court has outlined the built-in potential for mistaken or uncertain diagnoses in psychiatric evidence.

Some experts, the authors say, are so central to judicial decisions there is “a danger that they become almost deciders of the case”.

Unlike other witnesses, experts are paid and some make a living from court appearances and investigations, they note.

To ensure judges retain the decision-making power, they urge the strict application of rules governing expert testimony that have been shown to uphold judicial authority and a “fact-based” approach by judges when it comes to analysing what experts assert.

The judge should grasp the fundamental elements of the arcane discipline subject of the expert evidence and require the expert’s opinion to be founded clearly on an explanation of the science informing that. The aim is “to return independence” to the judge.

It is not the role of an expert to take over a court but that is “a real danger”, the authors warn. There is “a fine line between pushing an opinion and saying all that is necessary to support an opinion”. The latter is what a court needs and “should require”.

Unless the court has ability to analyse the basis for an apparent opinion, a judge “endangers judicial independence”. An opinion from an expert cannot be “just accepted”.

When a judge is determined, through using as much as possible of what is explained to the court, to retain and assert objectivity and independence, experts are both kept at a distance and their help is engaged.

There are dangers in expert evidence “but they need not, and should not, overwhelm the judicial function”, the authors conclude.