2.13 Expert Opinion is a type of evidence presented in a court of law. It is the opinion of a witness who is qualified as an expert in their field, and who has been formally accepted by the court as an expert witness. Expert Opinion is often used in complex cases, where the facts of the case require a more in-depth understanding of a particular subject. Types of Expert Opinion include medical expert opinion, financial expert opinion, engineering expert opinion, and legal expert opinion. Expert Opinion is considered to be highly persuasive evidence in a court of law and can be used to establish liability or to provide an explanation for certain facts or events.