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In Court, Predictivity Is the Gold Standard : Evidence: What makes scientific findings admissible is validity of the message, not qualifications of the messenger.

April 12, 1993|GIO BATTA GORI | Gio Batta Gori is director of the Health Policy Center, a research organization in Bethesda, Md.

Last month, the Supreme Court heard arguments on a case to update the rules about what is scientific evidence admissible to a jury. These rules have raised questions because they aim at validating the credentials of witnesses rather than the scientific substance of the evidence. Beyond judicial matters, any decision of the court will also influence the objectivity of the wider social debate that defines the American Way in this country and abroad.

The case is Daubert vs. Merrell Dow and the allegation is that Bendectin--a morning-sickness remedy--causes birth defects. Lower courts have dismissed the claim, finding that it is based on an unpublished review of previous studies.

The decision by the Supreme Court to hear the case prompted the filing of numerous amicus briefs, many of them from scientists. Far from being unanimous, the scientists appear as divided as ordinary mortals. Some argue that any speculation be considered scientific if it comes from people who fancy themselves as scientists. Others endorse the more benign but still uncertain notion that publication in scientific journals and peer consensus certify scientific evidence.

Division among scientists should not surprise. The coveted name of scientist has been seized even by people who hold that rhetorical skills alone certify knowledge. To make sense of it, the court will have to revisit those intellectual foundations that permitted the manifold contribution of science and scientists to our civilization. Undeniably, such foundations rest on the objectivity of demonstration, with the aim of predicting natural happenings.

Reliable predictivity is the unique hallmark of science and the determinant of its success. Science also introduced objectivity as the decisive measure of enlightened discourse in human affairs. Objectivity and predictivity distinguish science from the humanities and other fields where understanding depends on debatable dogmas and subjective interpretations.

Does science have all the answers? Obviously not. Science continuously expands our understanding of nature by proposing provisional hypotheses of cause and effect. Their validity is explored by sifting through the maze of experimental observations, toward restricting the probability of alternative explanations. Predictive power is the ultimate benchmark. If a hypothesis passes these tests it becomes accepted knowledge to explain the facts on hand. Hence, at any given time science displays a range of ideas at different stages of validation.

At which stage of validation is a hypothesis ready to be admissible scientific evidence in a jury trial? Considerations of fairness suggest that only validated predictive knowledge should be admissible, since immature hypotheses inevitably introduce unresolved uncertainties. If expert scientists are unable to overcome uncertainties, how could a lay jury do so impartially and objectively? Indeed, uncertainties cannot be resolved even by contrasting "expert" opinions. Such debates would still amount to verbal skill duels, and not to scientific clarification. The same would be true for hypotheses untimely approved by peer consensus alone, without demonstrable predictivity.

Take the case of Bendectin. About 30 studies of babies born to mothers who used Bendectin failed to uncover a causal connection with birth defects. A later analysis of these studies claims to have detected an association by restacking the combined results in a particular way. Which is the right interpretation? The dilemma arises because birth defects--like cancer, cardiovascular, and other multifactorial diseases--can be triggered by several known and unknown agents. Especially when the presumed effects are barely measurable, it is impossible to indict any agent with any degree of objectivity. For Bendectin, a causal implication could be reached only by the assumption--factually unwarranted--that everything else in the children studies has equal weight and cancels out.

Clearly, all this does not advocate excluding scientists from legal debates. At issue here is what gets to a jury. In reality, courts will still need pretrial hearings of experts to sort opinion from scientific evidence. This is where uniform guidelines from the Supreme Court are needed, giving prominence to the validity of the message rather than to the qualifications of the messengers. In such guidelines, predictivity should remain the gold standard and the indisputable guarantee of fairness in presenting scientific evidence to a jury.

Unfortunately, official policies have been often distorted by a pervasive corruption of science in the name of unspecified feelings, concerns and prudence, and with the complicity of many who call themselves scientists. Attributing the objectivity and impartiality of science to essentially arbitrary and factional policies and opinions has proven irresistible, and a habit that has dulled the collective responsibility to fairness. Arguably, it has become an insidious tool of oppression and a menace to a free society.

The Supreme Court has a unique opportunity to restore a sense of truthfulness and objectivity to the social dialogue, and to check the tide of private and official opportunism that threatens a return to the injustices of darker times.

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