The admission of expert testimony is subject to judicial approval, based on the expert's qualifications and the information on which they base their expert opinion. The federal rules of evidence provide courts with a framework they may reference when determining the basis from which experts can give an opinion. According to Federal Rule of Evidence 703,
Expert opinion may be based on facts or data:
(1) actually seen or heard by the expert or
(2) communicated to him at or before the hearing. Admissibility of the facts or data is not essential if typically relied on in this field.
How an Expert Acquires Facts or Data in Medical Malpractice Cases
There are four recognized ways in which an expert may acquire data on which to base his or her opinion in the case.
- by supposition at the trial (the hypothetical question);
- by listening to the testimony of other witnesses at trial;
- by personal experience before the trial, as in the case of a doctor testifying about a patient whom she has treated personally; or
- by being informed of data by others before the trial (hearsay)
Hypothetical questioning is one of four ways the Federal Rules of evidence offer for forming the basis of expert opinion. A witness, during questioning, may be asked if Facts A, B, and Q are correct. Based upon those facts, the witness will be asked their opinion. This allows for very pointed cross-examination, at which point the opposing counsel can hypothetically change, add or delete facts and ask the witness to reformulate their opinion based on these alterations. Hypothetical questioning may be used constructively however it may also be abused. Certain hypothetical questions may also be subject to a great deal of complexity, as one question cited by a Harvard publication saw a hypothetical question consume hundreds of pages of the court transcript.
Using the testimony of other witnesses is a practical method of data acquisition with certain notable drawbacks. The expert would be required to sit in court while listening to the testimony of other witnesses, which would undoubtedly prove to be an expensive endeavor, as experts charge a hefty fee by the hour. Moreover, relying on data acquired through witness testimony could present problems for the construction of an expert's opinion, if and when there is conflict or ambiguity in that witness's testimony.
An expert's personal experience can prove to be the most effective basis of testimony. Depending on the form of expertise, their personal experience may or may not prove efficient or sensible to undertake all tests and analyses of the evidence on their own. Those who performed tests or analyses themselves would have been called on for the expert in question to construct their opinion. For this reason, hearsay became a recognizable and legitimate basis of expert opinion.
The fourth method of hearsay allows the expert to develop an opinion based on facts of the case “made known to him or her” prior to the hearing. Hearsay is still subject to certain guidelines, as it must be reasonably relied upon by experts in the same field.
Facts and their Admissibility as Evidence
Further elaborating on the basis of opinion testimony by experts, Rule 703 states: 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.
The idea that opinion-supporting facts need not be admissible as evidence seems troubling at first glance, but is meant to guard testimony which was based on evidence that met the bare minimum requirement ("[evidence] of a type reasonably relied upon by experts in the particular field in forming opinions.") This effectively casts aside the hearsay rule, which prevents of out of court statements from being used to support arguments in court. With this exception, the expert witness becomes an important tool for allowing the attorney to present otherwise inadmissible evidence to the jury. If the expert is confronted with the option to make statements with inadmissible evidence, it is within their discretion to accept or reject the disputed evidence. In effect, they become a de facto additional juror, "trying the fact" presented by the attorney but on a private level.
Although the expert may present an opinion based on inadmissible evidence, they may not relay the evidence on which they founded that opinion to the jury. The situation raises certain difficulties, as the court essentially asks the jury to accept the expert's opinion without accepting the information that led them to form it. Depending on the context, such a proposition seems nonsensical. Hearsay is not necessarily false information, although it can be; so testimony based upon hearsay is not necessarily dubious, it is simply not subject to the same court-mandated treatment formalizing what was said/asserted.