Although the ultimate decisions that are made by judges and juries are based on facts, those facts are open to interpretation. Lay witnesses, meaning those who possess no additional knowledge than the average person, can testify to their personal knowledge and observations, but their testimony regarding their opinion is limited in scope. This is why it is often helpful to have expert testimony when dealing with complex issues. The testimony of these individuals can carry great weight and make the difference between winning and losing a case.
One of the greatest benefits of an expert witness is that he or she can provide opinion-based testimony even if it is based on evidence that is not otherwise admissible. Therefore, a witness who is qualified as an expert can base his or her opinion on hearsay, for example. This can open up the evidentiary gates and allow a powerful opinion to be presented even if other evidentiary issues exist. These experts can sometimes provide testimony that directly speaks to the legal issue at hand.
Not every professional is considered an expert, though. An individual must qualify an individual as an expert witness by asking questions and eliciting answers that demonstrate that the witness possesses specialized knowledge, training or experience. There is no bright-line rule when it comes to who qualifies as an expert, so the matter is often open to legal argument.
Choosing an expert witness is no easy task, either. This is because not every expert witness presents well on the stand and can testify in a way that is understandable and persuasive to lay jurors and a judge. For this reason, attorneys who are experienced in litigation and appeals carefully vet their potential expert witnesses to ensure they are going to have someone who can truly further their client's position.
Experienced legal professionals are often needed to combat the other side's expert witnesses, too, which can define the way the case is decided. With so much at stake, those who are amidst a case where an expert opinion may sway the outcome should consider discussing the matter with an attorney who is skilled and experienced.