What is Considered “Junk Science” From Expert Witnesses?

Not all scientific evidence is created equal. Researcher biases and idiosyncrasies, poor scientific procedures, errors in reasoning, or debunked theories all fall under the heading of “junk science.” Like junk food, junk science is devoid of substantive, useful content—no matter how appealing it might seem in the moment.

Expert witness standards have often been aimed at eliminating junk science from courtroom trials. Both the Frye and Daubert standards seek to improve the quality of expert witness testimony by screening out bad science and similar poor practices. Their respective means of achieving this goal, however, can vary dramatically.

Junk Science Under Frye

Prior to Frye v. United States, experts and their testimony weren’t always subjected to an admissibility test. When they were, the test was often pragmatic, even economic in nature: The witness was an “expert” if they could make a living doing what they did. If a specialized issue in that field arose, the witness could testify not only to facts but also to opinions informed by their profession.

In 1923, Frye focused on the use of blood pressure-based lie detector tests. The court affirmed that “experts or skilled witnesses” and their opinions were admissible in cases in which “inexperienced persons are unlikely to prove capable of forming a correct judgment,” because the subject matter is arcane, complex, or specific.

Frye gave judges considerable leeway in deciding which types of experts and expert testimony would be allowed in a particular case. However, the court set one standard: “the thing from which the deduction is made must be sufficiently established to have gained general acceptance in the particular field in which it belongs.”

Junk Science Under Daubert

After Federal Rule of Evidence 702 appeared in 1975, debate raged as to whether Rule 702 had done away with Frye’s “general acceptance” standard. Rule 702 allowed expert witness opinions from a witness “qualified as an expert by knowledge, skill, experience, training or education,” as long as that opinion – and the “scientific, technical, or other specialized knowledge” it contained would help the trier of fact understand the evidence or facts in issue. Daubert v. Merrell-Dow Pharmaceuticals sought to answer this question, along with others.

One of Daubert’s goals was to provide a means by which to reduce the likelihood of junk science entering the courtroom. Today, Daubert hearings function as a means to screen expert testimony, filtering out the worst of the bad science by demanding reliability and relevance from expert witness testimony.

In 2000, Rule 702 was amended to incorporate the requirements for expert witness testimony set forth in Daubert. These requirements allow expert witness testimony in the form of an opinion or otherwise, so long as:

• The testimony is based upon sufficient facts or data
• The testimony is the product of reliable principles and methods
• The witness has applied the principles and methods reliably to the facts of the case

What Are the Boundaries of Junk Science?

While the demands of Daubert and Rule 702 are more well-defined than Frye’s “generally accepted” standard, all three approaches continue to leave substantial leeway, particularly when it comes to presenting competing scientific theories in the courtroom.

While scientific research seeks results that are reproducible, falsifiable, and have predictive power, all scientific fields are in a state of continual growth and development. Hypotheses arise, are tested repeatedly, and over time are either discarded, amended, or rise to the more reliable level of theories. At any given time, the results of one or more studies may be explained by two or more competing theories as to the origins of those results, their causes, or outside factors that may influence them.

For instance, in In re Accutane Litigation, patients who had both taken Accutane and developed inflammatory bowel disease sought to have expert testimony admitted that would draw a causative connection between Accutane use and IBD. In February 2015, after expert witness hearings, the trial judge barred the experts’ testimony on the grounds that it was, effectively, junk science.

The New Jersey appellate court, however, reversed the ruling, stating that “the data was sufficient to permit the experts to testify, and any weaknesses in their opinions can be explored through cross-examination.” According to the appellate court, the question wasn’t whether the science itself was junk, but whether the jury would find the plaintiffs’ or defendant’s experts more credible—a decision that it was not the trial judge’s place to make.

Similarly, in recent litigation brought against Johnson & Johnson regarding its talc-containing baby powder, eight days of Daubert hearings focused on whether the plaintiff’s theory—that perineal application of the powder increases the risk of ovarian cancer—was backed by sound evidence or was simply more junk science. Five expert witnesses for the plaintiffs opined that the causative link was supported by the available evidence, while three expert witnesses for the defense opined that it was not.

Since many scientific issues have yet to be studied in detail, courtrooms are likely to remain the scene of arguments over competing theories in the future. Such arguments blur the boundaries between science that is clearly junk and science that is simply undeveloped or developing—making the admissibility of experts on both sides of these questions a tougher challenge.