By Dr. Ken Broda-Bahm:
There comes a moment in each expert's testimony where the actual opinions are delivered, and they're always delivered with something like this build-up: "I can say to a reasonable scientific certainty that...." In physician malpractice cases, substitute the word "medical" for "scientific." That is the legal standard, but what does that phrase really mean? And, particularly when an expert on the other side is using the same phrase to frame an opposite conclusion, how should a jury understand and apply it? The law doesn't seem to give much guidance on this point, since the standard is required but not defined. So it is left to the experts themselves to come to their own understanding of what "reasonable certainty" means. And it should come as no surprise that there is some inconsistency in the ways different experts will understand that phrase.
That is the conclusion of a recent study investigating what experts mean by "reasonable certainty." A group of researchers from Penn State College of Medicine (Dias et al., 2015) surveyed 294 medical specialists who testify about head trauma in cases of suspected child abuse, and found a relatively high diversity of meanings that the experts apply. The researchers found that while there were some commonalities in the way the experts would operationalize that standard, there was a significant amount of variability as well. For the greatest number, "reasonable certainty" means a 90 percent chance or greater that the claim is true. But for other experts, reasonable certainty could be found at the level of 50 percent or even lower. The lead author, neurosurgery and pediatrics professor Dr. Mark S. Dias, commented in ScienceDaily that "The juries think that everybody's testifying to the same degree of certainty, and that may not be true." He continues, "Knowing that one expert defines their degree of certainty as 98 percent and the other defines it as 50 percent would help the jury." In this post, I'll take a look at the study and share some ideas on how it can be applied to your preparation of your own expert as well as your cross of the opposing expert.