ABSTRACT
It is a long-standing principle that a witness is called to testify about facts and not about any opinions which they may have formed from those facts. A distinction between fact and opinion justifies the rule. One category of opinion evidence that is of increasing importance is that of expert evidence. This forms the principal exception to the general rule against the use of opinion evidence and allows an expert to give the court the benefit of their expertise. The treatment of DNA evidence continues to be an important aspect of expert evidence. In criminal cases, expert evidence on a particular matter is sometimes excluded on the grounds that it would be providing an opinion on the ultimate issue. Judges recognise that a psychiatrist or psychologist may be able to provide useful testimony on matters that are outside the experience of the judge or jurors.
