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What is an expert witness?

Dr Jan Wise, BMA medico-legal committee chair, discusses the role of an expert witness

An expert witness is a person who is qualified by their knowledge or experience to give an opinion on a particular issue to a court.

Their role is to assist the court on specialist or technical matters within their expertise.

The expert's duty is to the court. This overrides any obligation to the person who is instructing or paying them. This means that they have a duty to act independently and not be influenced by the party who instructs or pays them.

The main trait of expert evidence is that it is opinion evidence. However the expert is expected to take care not to express opinion that strays beyond the limits of their personal expertise.

Where opinions cross the boundaries of expertise, the expert is expected to respect and where appropriate defer to the opinions of experts in those other areas of expertise.

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