Expert opinion is valuable in many cases, but it can also be misguided. If an expert’s conclusions are based on faulty information, or if an expert’s expertise is otherwise limited, the results of their testimony could be harmful to your case. Therefore, it is essential to understand how experts are qualified to testify in your jurisdiction and how to evaluate the accuracy of their opinions.

The rules governing expert testimony vary by jurisdiction, but in general, experts must be able to articulate the basis for their opinions. In addition, experts must typically present a written report that includes all assumptions upon which the expert relied when writing the report. While a lawyer cannot control the assumptions that an expert may make in writing their reports, they can limit them by ensuring that the experts they hire are as qualified as possible to give accurate and persuasive opinions.

While experts must be given access to the facts of a case, they are not allowed to base their opinions on matters that are not supported by evidence or are speculative. Thus, during cross-examination it is important to question the expert about all information that he or she reviewed in order to determine whether the expert’s opinions pass the “Sargon” test of Rule 705 and are credible.

It is also important to note that the cloak of attorney work product that surrounds attorney-client communications is removed once an expert is hired as a witness. Thus, if an expert consultant has been retained with the intention of turning him or her into a witness, the attorney’s discussions with the expert must be made available to the opposing party on cross-examination.