The use of expert witnesses in litigation is something all litigators know to be commonplace. Some estimates suggest that roughly 30% of ALL federal cases use experts. Some types of cases (mass torts, environmental law, etc.) have almost mandatory requirements for using expert witnesses.
Litigators also know that a good expert has a couple of essential traits that really go beyond the actual expertise. An expert must be credible to a jury, who in complicated cases, may not fully understand the science being presented, but must still make a decision of enormous consequence. In the same vain, the expert must be confident in the courtroom. Juries generally find waffling and imprecise explanation to be a sign of weakness, and accordingly discount an expert’s testimony.
Yet, a third, and perhaps most critical, factor can make a difference in a jury’s perception of expert testimony: bias. How does a jury come to terms with two experts who disagree on fundamental questions of science, and who they perceive as being paid to testify? Indeed, it is precisely this bias that requires an expert to be credible and confident – juries have no other way of “breaking the tie.”