Expert witnesses in court cases must not be advocates for one side or the other but objective and fair, according to the High Court judge, Mr Justice Barr.
"It is important to bear in mind that the function of the advocate differs fundamentally from that of the expert witness," he told a conference for expert witnesses organised in Dublin by La Touche Bond Solon.
The company trains doctors, engineers and other experts in writing reports and presenting their evidence in court and publishes advice on marketing their services.
"The function of the expert witness is to advise the court as to his/her objective professional assessment of a given situation based upon established facts and specialist information and learning," said Mr Justice Barr.
He advised the audience, many of them doctors who give evidence in court cases, that the criteria they should adopt should be the same as when lecturing students on the probable consequences of a particular injury.
He warned that new rules of court arising out of the Courts and Court Officers Act, 1995, might create potential problems for expert witnesses.
Under these rules documents such as medical and other expert reports had to be shared by both sides, apart from certain specific exceptions. The rules are intended to allow for the identification of areas of agreement between the sides, thereby cutting down on court time and costs.
They will mean that expert witnesses appearing for an accident victim, for example, have to be aware that some of their evidence could undermine the victim's case for compensation, according to Mr Justice Barr. If it was relevant, it had to be included and would therefore be available to the other side. It would be up to the expert to decide whether it was relevant.
Mr Roderick Bourke, a solicitor, said the new rules meant that in injury cases expert issues would have to be assessed earlier and more thoroughly. Mr Justice O'Flaherty of the Supreme Court stressed the importance of impartiality, saying that judges and experts had much in common as both were the servants of justice.
He urged experts to keep meticulous records and to communicate their knowledge and conclusions in language a lay person would understand. Mr Timothy Scannell, an orthopaedic surgeon, welcomed the judges' emphasis on impartiality. He appealed from the floor for a system where the fees of expert witnesses were paid into a fund at the beginning of the hearing, to assist the expert in giving his or her evidence impartially.
"The system at the moment is that we are paid by one side in a case. If a person injured in a road traffic accident was not wearing a seat belt or had drink taken the award can be reduced. I find that fees can be reduced pro rata. That can induce the expert to slant his evidence."