“Trust the science” is a common phrase these days, but what exactly is science? This question comes up frequently for lawyers and judges involved in trial work, because of the use of “expert witnesses” to prove or disprove claims.
Most juries, like most people, give more weight to opinions expressed by experts. Thus, the courts have established a set of rules to determine who can testify as an expert. I think this can help as we try to decide who we should trust on the many issues that arise in our daily lives—particularly, issues of public health.
Both state and federal trials are governed by Rules of Evidence, and a very important one is Rule 702. This rule tells us when expert testimony is allowed: “If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue”; and who is considered an expert: “a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise.”
In addition, courts and legislatures have established rules about when expert testimony is required: when “scientific issues would be beyond the capacity of men of common experience and knowledge to form a valid judgment by them- selves … expert evidence [is] required to assist a jury in its decision.” (from a 1974 opinion, when gender-neutral terms were rarely used). An even older case explained, “courts should not leave it to a jury of tailors and haberdashers to pass judgment [unaided by expert testimony] on how to make a wet and rolling deck in a seaway a safe place to work.”
The most common examples of cases where expert testi- mony is required are those involving medical malpractice, personal injury, and workers’ compensation. There are also several examples of cases where expert testimony has not been allowed, either because the witness is not qualified— for example, a police officer with no medical training being asked to testify about the cause of a victim’s injury—or when a witness has impressive qualifications, but has not followed accepted scientific principles in reaching their opinions. A frequent example of that is in criminal cases involving sexual abuse.
In the New Hampshire case which established the princi- ple that expert testimony must be “reliable,” a psychologist’s testimony that a child had been sexually abused was based solely on interviews of the child. Thus, rather than simply allowing the jury to draw its own conclusions about the child’s testimony, the prosecution sought the added advantage of testimony from a “highly qualified expert” that, essen- tially, the child’s testimony was true. The New Hampshire Supreme Court reviewed the psychologist’s methodology and concluded that it was not based on any standardized tests or quantifiable results which would allow a court or cross-exam- ining attorney to test the validity of her conclusions, and was therefore not reliable.
Reliability includes the concept of “testability,” also referred to as “falsifiability” or “refutability.” This is import- ant in the analysis used by federal courts in deciding whether to allow expert testimony. The United States Supreme Court discussed the standards to be used in a decision known asDaubert v. Merrell-Dow. The court instructed judges to consider “whether the theory or technique in question can be [and has been] tested, whether it has been subjected to peer review and publication, its known or potential error rate, the existence and maintenance of standards controlling its operation, and whether it has attracted widespread acceptance within a relevant community.”
“Testability” refers to whether it is possible to test an expert’s statement to show that it is false. For example, if an expert testifies that all people with the last name Brown have brown eyes, it can easily be disproved by finding someone named Brown with blue eyes.
A more scientific example recently in the news was when our state epidemiologist testified that 90% of people hospitalized with COVID-19 are unvaccinated, a statement that is “testable” because it is possible to prove, or disprove it, by surveying all the hospitalized Covid patients. However, this would be difficult and costly, which is why another way of confirming the validity of expert opinions is determining whether it has been studied by other experts and discussed in scientific literature. That is the case for this statement as we know the CDC and many other organizations have collected and published this data.
Making sure that only qualified and reliable expert testimony is allowed in civil and criminal trials has become so important that the Federal Courts have published a 630-plus page reference manual on scientific evidence outlining the factors involved in various types of scientific testimony, such as epidemiology. This is the field most important in under- standing the COVID pandemic and how it can be stopped; I encourage anyone who has an interest in learning more about this science to read the manual, which is available online.
The internet and social media are filled with claims of “scientific facts,” which, unfortunately, are often based on little more than the writer’s personal opinion or unverified anecdotal circumstances. I hope that this explanation of the principles the courts follow to evaluate such claims will help you make your own decisions about their validity.