An expert witness is a
witness, who by virtue of
education,
training,
skill, or
experience, is believed to have
knowledge in a particular subject beyond that of the average person, sufficient that others may officially (and legally) rely upon the witness's specialized (scientific, technical or other) opinion about an
evidence or
fact issue within the scope of their expertise, referred to as the expert opinion, as an assistance to the
fact-finder. Expert witnesses may also deliver expert evidence about facts from the domain of their expertise.
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Sworn trial or pretrial statements from a qualified specialist held to be an expert on a subject relevant to the case.