Unlike lay opinions, expert conclusions are based on specialized knowledge and training that help fact-finders understand complex issues in cases. To be admissible, however, such opinions must follow a specific framework and avoid transgressing certain boundaries. This article explores the scope and limitations of expert opinion, including what experts may testify to, on what information they can base their opinions, how confident experts must be in the “correctness” of their opinions, and what kinds of case types experts most often appear in.
When preparing for testimony, experts should make every effort to ensure that their opinions are reliable and well-supported by the facts of the case. Doing so can help ensure that the expert’s conclusions are valid, withstand challenge by opposing counsel, and are credible to the jury. Experts should also avoid making statements based on anecdotal information or relying upon a single design choice (i.e., “my opinion is that this option is the best one”). Such a statement can be challenged by opposing counsel on cross-examination as being unsupported and biased.
Additionally, while it is not necessarily a requirement that an expert produce a draft of his or her report prior to its finalization, it is generally a good idea to do so. This can prevent an expert from being surprised by the content of the report or the questions posed on cross-examination. This can also reduce the number of last-minute revisions that many experts are forced to undertake.