(a) The facts or data in the particular case upon which an expert bases an opinion or inference may be those perceived by or made known to the expert at or before the hearing. If of a type reasonably relied upon by experts in the particular field in forming opinions or inferences upon the subject, the facts or data need not be admissible in evidence.
(b) Underlying expert data must be independently admissible in order to be received upon direct examination; provided that when good cause is shown in civil cases and the underlying data is particularly trustworthy, the court may admit the data under this rule for the limited purpose of showing the basis for the expert's opinion. Nothing in this rule restricts admissibility of underlying expert data when inquired into on cross-examination.
(Amended effective January 1, 1990.)