Expert evidence in US litigation

Expert evidence plays an important role in modern US litigation. Under Rule 702 Testimony by Expert
Witnesses:
"A witness who is qualified as an expert by knowledge, skill, experience, training, or education may testify
in the form of an opinion or otherwise if:
(a) the expert?s scientific, technical, or other specialized knowledge will help the trier of fact to understand
the evidence or to determine a fact in issue;
(b) the testimony is based on sufficient facts or data;
(c) the testimony is the product of reliable principles and methods; and
(d) the expert has reliably applied the principles and methods to the facts of the case."
Under Rule 703 Bases of an Expert?s Opinion Testimony
"An expert may base an opinion on facts or data in the case that the expert has been made aware of or
personally observed. If experts in the particular field would reasonably rely on those kinds of facts or data
in forming an opinion on the subject, they need not be admissible for the opinion to be admitted. But if the
facts or data would otherwise be inadmissible, the proponent of the opinion may disclose them to the jury
only if their probative value in helping the jury evaluate the opinion substantially outweighs their prejudicial
effect."
In Daubert v Merrell Dow Pharmaceuticals Inc 509 U.S. 579 (1993),it laid down a framework for the
application of the Evidence Rules to scientific expert
testimony and focusing on the standard for admissibility of scientific expert testimony. The principles and
methodology from which the expert
testimony was derived should be both relevant and reliable, other the opinion would not be admissible.
In Khumo Tire v Carmichael 526 US 137 (1999), it extended Daubert further to all non-scientific expert
testimony, that is, to all technical or specialized knowledge. In other words, ?expertise? may be plainly
derived from ?experience? and not necessary from scientific methods.