Evidence: Testimonial Evidence: Witnesses: Opinion Testimony by Expert Witnesses

• Opinion testimony by Expert Witnesses: An expert may state an opinion or a conclusion provided:

• The witness is qualified by education or experience;
• The testimony is about a subject matter where scientific, technical, or specialized knowledge will be helpful to the jury;
• The opinion is reliable;
• The opinion has a proper basis.

• Proper basis: Based on "reasonable degree of probability" or "reasonable certainty" and the opinion is based on (1 of 3 data sources):

• The expert's personal knowledge;
• Evidence that is already in the record;
• Facts outside the record but only if those facts are of a type reasonably relied upon by experts in the particular field.
• (Note: if expert relies on facts outside the record, he may generally discuss the basis of the opinion, but may not disclose inadmissible facts to the jury—the opponent, however, may disclose the underlying basis on cross examination)

• Reliability: To be admissible the expert opinion must be sufficiently reliable ; the expert must have used reliable methods and reliably applied those methods to the particular facts of the case.

• Reliability Standard for Scientific Evidence
• Federal Rule-Daubert: Court examines reliability by considering:
• Has the methodology been tested?
• Are there known rates of error?
• Has the methodology been subject to peer review?
• Has the methodology been generally accepted?