Expert opinion is the informed perspectives and conclusions of individuals who possess specialized knowledge, skills, or experience in a particular field. Expert opinions can provide a valuable addition to arguments, lending credibility and weight to claims while also helping to address counterarguments.
Whether an expert has a reasonable degree of scientific certainty that his or her opinion is correct is often at the heart of an expert’s testimony. This can be a common topic of cross-examination and is an area where careful research and preparation can help to protect the credibility of an expert’s opinion.
Experts must also be aware of and understand the governing legal environment in which they work, including statutes, regulations, codes, standards, and guidelines that may impact the validity or reliability of their opinion. Moreover, experts should be prepared to cite and produce documents containing the facts or data on which they relied in forming their opinion.
There are three possible sources of the information on which an expert’s opinion is based: (1) firsthand observation (as in a treating physician); (2) the expert’s knowledge of the evidence in the case (as in hypothetical questions or a presentation at trial); and (3) other available information. Courts have taken differing positions on how to treat information that would be inadmissible if offered as direct evidence, but that an expert reasonably relied upon when forming his or her opinion or inferences.
For example, in epidemiologic assessments, particularly veterinary disease freedom surveillance, empirical information is often limited and costly to obtain. However, experts may be able to synthesize information through long, cumulative experiences such as anecdotal observations that natural food supplies have remained stable, increased human-bear conflicts, or reports of known poachers being apprehended.