Parties to any dispute who rely exclusively on opinions of experts without establishing the factual basis for those opinions do so at their peril.

The opinion of an expert must be based on facts that are established by the evidence. The court then assesses the opinions of experts on the basis of ‘whether and to what extent the opinions advanced are founded on logical reasoning’.

As a first step, however, the court must consider whether the underlying facts relied on by the witness have been established. If not, then the expert’s opinion is worthless as it is purely hypothetical. In such a case the opinion will be disregarded. Once the facts are established the court is required to consider whether the expert’s view is one which can be reasonably held on the basis of the established facts. The court examines the reasoning of the expert and determines whether it is logical in the light of those facts and any others that are undisputed or which cannot be disputed.

While a party can usually call witnesses in any order it likes, it is usual practice for expert witnesses to be called after other witnesses so that they can express opinions on the facts dealt with by those witnesses. Proper evaluation of the expert’s opinion can only be undertaken if the process of reasoning which led to the conclusion, including the premises from which their reasoning proceeds, is disclosed by the expert. An opinion based on facts which are not in evidence has no value for the court.

Where there are competing expert views it would be wrong for a court to decide a case by simple preference where those views are both capable of logical support. It is only where expert opinion cannot be logically supported at all that it will fail to provide ‘the benchmark by reference to which the defendant’s conduct falls to be assessed’.

The approach to expert evidence was revisited and restated in the recent Supreme Court of Appeal judgment of the Road Accident Fund and Sihle Madikane including the court’s application of the law to the facts of the case. The court determined that contrary to the views of the trial court there was no admissible factual evidence to support the conclusions drawn by the claimant’s medical expert witnesses. Their opinions lacked the requisite factual foundation that our courts consistently demand must be the basis for expressions of opinion by an expert.

This approach to expert evidence was again visited and again stated by the High Court of KwaZulu-Natal in AD v MEC for Health for the Province of KwaZulu-Natal. That court also pointed out the fact that all the defendant’s experts were employed by the defendant and could therefore have some loyalty or sympathy for their employer, and this could not be ignored altogether in considering the expert evidence.