Lay witnesses testify about what they saw, they heard or they smelled. Lay witnesses are restricted in giving opinions unless the opinions that are being offered are of the type that don’t require specialized knowledge. Expert witnesses are different than lay witnesses. They can offer opinions on specific subjects within that expert’s expertise. New Hampshire court rules state that if scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise.

I have had the occasion to use an economist, an agronomist, a psychologist and many other types of experts in the courtroom. At the current time, I am planning to use a forensic accountant. Experts come in all shapes and sizes. A high school physics teacher can be an expert. So can an auto mechanic be an expert. One question that invariably comes up when using an expert is this – what is the bases of opinion held by the expert. The answer is that 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. Attorneys often frame hypothetical questions to an expert. In these hypothetical questions, the attorney asks the expert to assume that the facts in a hypothetical question are found to be true by the trier of fact (e.g., the judge or the jury).

In other words, the expert is asked to assume that a certain fact or set of facts is found to be true for the purpose of giving an opinion or two. Experts are then allowed to give opinions as if the trier of fact has found as true the facts in the hypothetical. If an attorney frames a hypothetical question containing a number of facts, the attorney better make a good faith effort to prove those facts. The best practice is to prove the facts first and then call the expert. Experts can testify by giving their opinions. They can also draw inferences from facts. Experts are required to give reasons for their opinions and/or inferences. If pressed, the expert has to disclose whatever facts or data they rely on for their opinions. In civil cases, New Hampshire law requires expert witnesses to be disclosed in advance ofthose witnesses testifying.

This disclosure requirement pertains to experts that are retained or specially employed to give opinions in a particular case. Experts generally provide signed, written reports before testifying. These reports include a complete statement of: (a) All opinions to be expressed and the basis and reasons therefor; (b) The facts or data considered by the witness in forming the opinions; (c) Any exhibits to be used as a summary of or support for the opinions; (d) The qualifications of the witness, including a list of all publications authored by the witness within the preceding 10 years; (e) The compensation to be paid for the study and testimony; and (f) A listing of any other cases in which the witness has testified as an expert at trial or by deposition within the preceding 4 years.

The court directs the timing of the disclosures. This is generally done by court order. The disclosures are usually due at least 90 days before a court date. A shorter time period is available if the expert testimony is intended solely to contradict or rebut evidence on the same subject matter identified by another party. It is imperative to supplement disclosures when supplementation is necessary. For example, if opinions expand, supplementation is necessary. If opinions change, supplementation is necessary. The idea is to make certain that the opponent knows what the opinions are when the expert witness takes the stand. This is only fair.

Depositions of experts often take place. Sometimes the deposition testimony becomes the trial testimony. In that way live testimony is avoided and unnecessary expense is avoided. An expert witness will not be allowed to offer expert testimony unless the court finds: (a) Such testimony is based upon sufficient facts or data; (b) Such testimony is the product of reliable principles and methods; and (c) The witness has applied the principles and methods reliably to the facts of the case. In evaluating the basis for proffered expert testimony, the court shall consider, if appropriate to the circumstances, whether the expert’s opinions were supported by theories or techniques that: (1) Have been or can be tested; (2) Have been subjected to peer review and publication; (3) Have a known or potential rate of error; and (4) Are generally accepted in the appropriate scientific literature.

Expert testimony has to be listened to carefully. This is because once an expert begins to give opinions, they can quickly get out of their field of expertise. This can’t be allowed and attorneys have to be vigilant in fighting such testimony. The court has to be vigilant as well. Experts play an important role in court proceedings.

It comes down to this – sometimes an opinion or two helps the trier of fact make sense of an otherwise complicated set of facts.