Admissibility v. sufficiency: the dilemma of expert evidence in toxic tort cases.

• Author: Linn, Stacy A.

If expert evidence without adequate epidemiological support is admitted, resulting unfair liability might drive needed products from the market

PLAINTIFFS suing pharmaceutical and medical device manufacturers often find convincing a judge and jury that a product caused their injuries very difficult. Manufacturers, on the other side, frequently find themselves liable for injuries that plaintiffs cannot prove were caused by their products. Part of this paradox arises because plaintiffs frequently sue manufacturers before the scientific community has determined whether a substance does or may cause certain injuries. The inconsistencies in results arise from the different amounts of clinical proof required by different courts. Nevertheless, both plaintiffs and the defendants rely on expert witnesses to opine that a substance did or did not cause an injury.

BASES OF EXPERT TESTIMONY

1. Frye Test

   Courts must determine what constitutes a valid basis for an expert witness's opinion when they rule on the admission of expert testimony. In 1923, the Circuit Court of Appeals for the District of Columbia announced the Frye test--that "while courts will go a long way in admitting expert testimony deduced from a well-recognized scientific principle or discovery, the thing from which the deduction is made must be sufficiently established to have gained general acceptance in the particular field to which it belongs."(1) The majority of American courts adopted that test, which eventually became known as the "general acceptance test." Even under Frye, however, courts could not agree on what constituted the "general acceptance" that would allow an expert to testify.

2. Federal Rules of Evidence

   In 1975, Congress enacted the Federal Rules of Evidence in an effort to simplify and liberalize the concept of admissibility.(2) Two of those rules, 702 and 703, specifically deal with expert testimony. Rule 702 allows "a witness qualified as an expert by knowledge, skill, experience, training or education," to testify "in the form of an opinion or otherwise," if "scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue." Rule 703 states: "The facts or data in the particular case upon which an expert bases an opinion or inference may be those perceived by or made known to the expert at or before the hearing. If of a type reasonably relied upon by experts in the particular field in forming opinions or inferences upon the subject, the facts or data need not be admissible in evidence." (Emphasis added.)

   After the advent of the Federal Rules, federal courts split sharply over whether the Frye test was still applicable in view of Rules 702 and 703. Some courts decided that the Federal Rules superseded Frye, and they began applying more liberal standards of admissibility.(3) There was particular disagreement over the type of research on which experts could rely to support theories of causation. These differences became especially apparent in the Bendectin cases.

   Finally, the U.S. Supreme Court agreed to decide whether the Frye test remained viable after the Federal Rules took effect, and it granted certiorari in Daubert v. Merrell Dow Pharmaceuticals Inc.(4) In that case, the Court rejected the Frye test as no longer proper under the Federal Rules of Evidence, and in an opinion by Justice Blackmun, it enumerated certain factors to be considered by courts when determining whether expert testimony is admissible.

3. Post-Daubert

   The Supreme Court intended Daubert to liberalize the rules on admitting expert testimony, as the Federal Rules were supposed to do, but a question remains whether Daubert has done so, and even whether Daubert should do so.

   Consider, for instance, what different types of studies actually prove and the difficulties of relying on non-epidemiological studies. Because in vitro and in vivo studies are not clear enough indications of causation, plaintiffs should not be allowed to introduce an expert witness's opinion based solely on those studies. Although courts should permit experts to testify to opinions utilizing these studies as part of the basis for their opinions, courts should require experts to include epidemiological studies in their opinions.

   Courts also have struggled with the question of how much epidemiological evidence is sufficient to prove a plaintiff's case. Again, the cases involving Bendectin have played a large part in this debate. Many courts, no matter what decisions on admissibility, require that a plaintiff merely submit some epidemiological evidence indicating that the substance causes an injury before they will rule that the plaintiff introduced sufficient evidence. Other courts require a higher level of scientific proof before a plaintiff can defeat a motion for summary judgment.

   Despite (if not because of) the liberal standards that should be applied in determining whether expert testimony is sufficient, a willing testifier alone is not sufficient evidence to support a judgment in favor of a plaintiff. Instead, a plaintiff should be required to prove that people who are exposed to a substance have more than double the incidence of the particular injury as compared to those who do not. With this type of statistical evidence, plaintiffs can show that it is more probable than not that the substance caused their injuries. Requiring more than double the incidence does not raise the burden of proof; it merely requires proof of causation by a preponderance of the evidence.

   Requiring plaintiffs to prove that the incidence of an injury doubles with exposure to the substance in question also prevents defendants from paying damages when plaintiffs have not proved that the defendant's product caused the injury.

   For illustration of the difficulties in determining whether expert testimony is admissible and sufficient to prove a plaintiff's claims, consider the Bendectin cases of the 1980s and the more recent breast implant cases. Courts have not been able to arrive at a consensus for admissibility and sufficiency in either of these fields of litigation, yet both products have been removed from the market despite the lack of evidence.

   BENDECTIN

   In 1956, Merrell Dow Pharmaceuticals Inc. introduced a new, anti-nausea drug marketed directly to women suffering from morning sickness. Bendectin was originally formulated from three drugs, one of which was an antihistamine.(5) Twenty years later, the first suits against Merrell Dow relating to Bendectin were filed, and ultimately they became so numerous that they were consolidated in multi-district litigation from which, however, plaintiffs could opt-out.(6)

   The plaintiffs uniformly claimed that Bendectin caused limb reduction birth defects.(7) Although some juries awarded them millions of dollars, trial courts or appellate level courts generally reversed those awards.(8)

   In response to the concerns about the safety of Bendectin when used during pregnancy, and possibly as part of the reaction to the tragedies surrounding the use of thalidomide, the Food and Drug Administration studied Bendectin extensively, as did scientists in other countries.(9) None of the studies performed by the FDA or other scientists showed any statistically significant connection between Bendectin and birth defects. Nevertheless, because of its potential exposure to huge amounts of liability, Merrell Dow stopped manufacturing and selling Bendectin in 1983.(10)

   The Bendectin litigants concentrated on the three types of studies used by scientists to establish the side effects of a substance --in these cases, limb reduction birth defects. The three studies are in vivo, in vitro, and epidemiological. In vivo studies are performed on live animals, usually rats or rabbits, to determine the effect of the drug or substance on that animal. In vitro studies use live cells from certain animals. The cells are placed in a petri dish or some other similar container with the substance being tested. In vivo and in vitro tests are useful for predicting whether the substance may have some harmful effects on that species, and the tests may indicate that epidemiological studies are warranted.(11)

   The primary criticism of in vitro and in vivo studies is that the dosages are usually far in excess of what the normal human being would ingest and that the cells and animals are exposed to the substance in an undiluted form. Additionally, different species metabolize substances in different manners. Scientists, therefore, cannot state with any certainty based on in vivo and in vitro studies that a substance that caused one specie injury will cause other species the same injury.

   In contrast, epidemiological studies monitor the reaction of humans to the substance being questioned to discover whether "there is an association between a disease or a condition and the factor suspected of causing that disease of condition."(12) In some studies, researchers will follow a group exposed to the substance to determine what similar injuries, if any, the exposed participants suffer. The main difficulty with those studies is that people who know they are being studied may be more likely to report illnesses and injuries than those who do not know they have been exposed to that substance.(13)

   In other epidemiological studies, researchers will select a control group that has not been exposed to the substance and another group that has been exposed. Then they will compare the illnesses of the two groups. In studies of Bendectin, for instance, the researchers generally compared the rate of birth defects in children whose mothers had taken Bendectin to those whose mothers had not. The result and accuracy of the research are measured by determining the relative risk and the confidence interval.(14)

   The relative risk is a...