Admissibility and reliability of expert scientific testimony after Daubert.

• Author: Livingood, Jr., John A.
• Position: Daubert v. Merrell Dow Pharmaceuticals, Inc.

THE PROLIFERATION of toxic tort litigation has strained the traditional tort concepts of causation. Litigants increasingly have to rely on expert testimony to prove, disprove or cast doubt on causation. Faced with the obligation to protect themselves and juries from unreliable or irrelevant evidence, courts attempt to evaluate the reliability and validity of expert evidence despite their general scientific ignorance. This situation has created confusion and spawned inconsistent results, demonstrating the need for some readily available source of information on the reliability and validity of various scientific methods that would enable courts to make educated and rational evaluations of expert evidence on causation issues.

In 1993 the U.S. Supreme Court responded to this confusion in Daubert v. Merrill Dow Pharmaceuticals Inc.,(1) which establishes factors to be utilized by courts when making a preliminary assessment of the reasoning and methodology employed by experts. In doing so, the Court expressly rejected the general acceptance test articulated in Frye v. United States(2) and utilized by courts for 70 years as the determinant of the admissibility of an expert's testimony.

PROVING CAUSATION

Toxic tort litigation creates unique causation problems because of the nature of the injuries typically suffered by individuals exposed to allegedly toxic substances.(3) Plaintiffs have two problems. First, they must prove that the substance to which they were exposed is capable of causing the alleged harm, a concept commonly referred to as generic causation.(4) Second, they must prove that the defendant's actions were the actual cause of the specific injuries. This is called specific causation or cause-in-fact, and it poses the daunting hurdle to the proof of causation.

Specific causation is often difficult to prove for numerous reasons. First, injuries frequently do not manifest themselves immediately because of a long latency period between contact with a substance and the resulting injury. It may be almost impossible to establish a causal relationship between an exposure and an injury that appears months, years or even decades later. Second, injuries caused by exposure to a toxic substance also can be found in background levels in the general population, forcing plaintiffs to prove that their injuries are specifically attributable to the toxic substance and not to the general incidence of the disease or injury. Third, plaintiffs also are faced with the problem of multiple generators of the allegedly injurious substance, thus requiring proof that the defendant's actions in fact caused the injuries.

Because of these problems, plaintiffs must rely almost exclusively on the testimony of experts to prove causation.(5) Experts employ scientific methods to provide evidence or theories of causation, especially when this information is not readily available from other sources. Challenges to the admissibility of expert evidence--generally by a motion in limine or for summary judgment--therefore represent challenges to plaintiffs' cases in chief. Generally, if an expert's testimony is not allowed, the case fails before trail.(6) Conversely, if the testimony is admitted, juries frequently award significant damages.

The testimony of an expert to a jury of lay persons presents certain problems. It is for this reason that courts must investigate the proffered expert's opinion, ensuring its validity and reliability.(7) Validity has been described as the accuracy of the scientific technique, ensuring that the procedure measured what it was supposed to measure, while reliability refers to the consistency of the procedure, ensuring that the same results will be obtained each time the test or procedure is performed.(8)

One of the main concerns created by the admission of experts' opinions is that the testimony will take on an aura of infallibility. A relatively uneducated jury, unfamiliar with the subject of the testimony, often views the expert as the definitive authority, giving the opinion greater evidential importance than factors such as validity, credibility and logic may warrant. Another peril is the lack of objectivity of many expert witnesses. Litigants usually choose experts who will unequivocally support their propositions regardless of the expert's belief in those propositions.(9) Finally, there is the danger that the jury's evaluation of experts' testimony will be affected by sympathy for the injured party.

PRE-DAUBERT INCONSISTENCY

Before the Supreme Court's decision in Daubert, there was little consistency in courts' evaluation of the admissibility of expert evidence.(10) The only real consensus was that Rule 104(a) of the Federal Rules of Evidence obligated the trial court to make a preliminary inquiry into the admissibility of scientific evidence, but from that starting point both courts and commentators diverged wildly.(11)

While courts seemed to take their own approaches, they generally employed one of two theories. On one extreme, they gave great deference to the testimony of experts, refusing to examine the scientific basis for experts' opinions. Under this analysis, courts examined the testimony only for relevance. If the proffered evidence was relevant and the court found the expert qualified, the evidence was admitted. The other approach involved strict judicial scrutiny of experts' opinion with an evaluation of the scientific methodology and principles supporting the opinion.(12)

These are important concepts, because a court's preference for either a deferential or strict approach often influenced its application and interpretation, or misapplication and misinterpretation, of various rules governing the admissibility of expert testimony. Stated less elegantly, courts often "bootstrapped" an interpretation of the common law and the Federal Rules of Evidence in order to conform to the courts' preconceptions regarding the relative value of the proffered evidence and proper role of the court in evaluating the evidence.

Federal Rules of Evidence 702, 703, and 403 and the Frye decision were most often cited when courts analyzed the admissibility of scientific evidence. These principles, however, were commonly miscunderstood and applied incorrectly by federal courts, leading to substantially inconsistent holdings among and even within circuits.

1. The Frye Test

   Frye represents one of the earliest and most influential judicial attempts to control the admission of scientific evidence. It established the "generally accepted by the scientific community" standard, providing a readily ascertainable source of information to a court faced with determining the scientific validity of an expert's opinion.(13) Its objective was to prevent "the introduction into evidence of specious and unfounded scientific principles or conclusions based upon such principles."(14) Because judges are not generally acquainted with the expert's theories or methodology, the "generally accepted" standard provided a useful, yet crude, measuring stick.

   Frye was a criminal case in which the District of Columbia Court of Appeals decided to exclude expert testimony on the results of a systolic blood pressure deception test, an early version of the polygraph. It articulated this famous (or infamous) test:

   Just when a scientific principle or discovery

   crosses the line between the experimental and de-

   monstrable states is difficult to define. Some-

   where in this twilight zone the evidential force of

   the principle must be recognized, and while courts

   will go a long way in admitting expert testimony

   deduced from a well-recognized scientific prin-

   ciple or discovery, the thing from which the de-

   duction is made must be sufficiently established

   to have gained general acceptance in the particu-

   lar field in which it belongs.(15)

   In applying the "general acceptance" theory, it is important to distinguish between an expert's methodology and conclusions. Only the methodology should be subject to scrutiny for general acceptance. An opinion that deviates from general acceptance but is based on generally accepted methodology and technique should be afforded deference and not excluded.(16)

   The general acceptance theory was utilized by courts as the standard for the admission of scientific evidence until the mid 1970s when Congress enacted the Federal Rules of Evidence, but it came under increasing criticism from both courts and...