NOTE: THE BASES OF EXPERT OPINIONS
Rule 703 recognizes four distinct ways for an expert to acquire the data on which he bases his opinion: (1) by supposition at the trial (the hypothetical question); (2) by listening to the testimony of other witnesses at trial; (3) by personal experience before the trial, as in the case of a doctor testifying about a patient whom she has treated personally; or (4) by being informed of data by others before the trial (hearsay).
Hypothetical Questions. The hypothetical question has the potential for carefully delineating the basis of an expert's opinion and for allowing precisely formed cross-examination. The question typically takes a form such as:
Q: Doctor, assume that the following facts are true: fact A, fact B, ... fact N. (Counsel poses all the relevant facts of his case as facts to be assumed.) Now, doctor, based on those assumed facts, do you have an opinion whether ...?
Q: What is your opinion?
A: My opinion is that ....
On cross-examination opposing counsel can then test the opinion by changing one or more facts, or adding or deleting facts, and asking how (or whether) the doctor's opinion is affected. For example:
Q: Doctor, assume that the car was travelling at 10 mph instead of 30 mph at the moment of impact. What then would be your opinion as to ...?
One problem with hypothetical questions is that while they may be used constructively, they also may be abused. With each statement of a hypothetical question counsel has an opportunity to reiterate the facts of his case, order them, and indicate their significance--in effect, to make a closing argument. Another problem is their potential complexity. One hypothetical question consumed nearly one hundred pages of transcript. What are the chances that the jury understood the question, or even kept awake through it?
Do the Federal Rules leave the option with counsel to use or not to use hypothetical questions? If so, have the rules failed to deal with the problem of abuse? What power does a federal trial judge have to stop a lawyer from using hypothetical questions in a manner that the judge considers abusive?
Other Witnesses. The difficulties with this method of data acquisition are both practical and theoretical. To acquire data by listening to other witnesses requires the expert to sit in court while the others testify, an expensive proposition. Moreover, if there is any conflict or ambiguity in the testimony of the other witnesses, the expert's data-base will be ambiguous and will require clarification.
Personal Experience. This, typically, is the most effective basis for testimony. A ballistics expert will be most effective if he has test-fired the weapon himself and made microscopic photos of the resulting grooves and comparison photos with the bullet. The problem is that with some forms of expertise it is neither efficient nor sensible for the expert to perform all tests or analyses himself. Unless the expert could rely on the work of others, those who actually performed the tests would have to be called to testify before the expert could give his opinion based on the tests. This problem led to recognition of hearsay as a fourth legitimate form of data-base.
Hearsay. As indicated by the Advisory Committee's notes to Rule 703, the most radical extension of this rule is its authorization for experts to rely on facts or data "made known to him" before the hearing--e.g., hearsay. The hearsay must be of a type reasonably relied upon by experts in the particular field in forming opinions or inferences upon the subject; but who is to make this determination and how?
Would the following reformulation of Rule 703 be an improvement on the present version or an unwise retreat from a useful reform?
An expert's opinion may be based on a hypothetical question, facts or data perceived by the expert at or before the hearing, or facts or data in evidence. If of a type reasonably and customarily relied upon by experts in the particular field in forming opinions upon the subject, the underlying facts or data shall be admissible without testimony from the primary source.