Introduction: In the conventional view, scientific fields advance through the concerted efforts of researchers dedicated to studying phenomena to better describe, predict, and not infrequently, control them. As basic research data accumulate, they often are applied to specific instances of the phenomena being studied. Meteorologists, for example, study weather systems to identify variables that will permit accurate forecasting of rain on a particular day, and geophysicists study earthquakes to anticipate when the plates along a given fault line will shift. Although the former have so far been more successful than the latter, the basic framework they employ is fundamentally similar: gather data from enough instances of the phenomenon in question so that in the aggregate they provide sufficient understanding to permit description, prediction, and (sometimes) intervention. In fact, this basic structure of scientific inquiry is consistent across the many disciplines interested in applying their data to real-world events, including engineering, medicine, economics—and, of course, the subject of this Article, psychiatry.
Despite the pervasiveness of the view described above, the scientific enterprise is not principally designed to provide categorical assessments of particular cases. Indeed, the focus of science is the analysis of aggregate data, and the language of science is statistics. Whether a scientist is studying violent storms or violent people, research findings are expressed in terms of likelihoods and probabilities. Meteorologists might be able to specify the likelihood that storms of the type bearing down on a particular city will evolve into a hurricane, and psychiatrists may be able to specify the likelihood that people who are similar in certain ways to a respondent in a civil commitment hearing will be violent in the future. But these are probabilistic assessments that can only inform—not determine with certainty—whether a city will be hit by a hurricane or whether a respondent will be violent. The degree of uncertainty becomes the operative question when science is applied to particular settings. In the forecasted hurricane example, the decision of whether to board up windows, ride out the storm, or evacuate the city will depend in part on the uncertainty of the forecast. When it comes to the prediction of violence, the decision to put a person who is mentally ill on a 72-hour psychiatric hold should similarly take into account the uncertainty of the prediction.
When science is used to make decisions about individual cases, it often requires categorical judgments to be made in light of the uncertainties of the general data. In medicine, treatment decisions are made after considering research on the success rates of possible treatments, which may differ between studies due to as-yet-unspecified variables. In engineering, particular buildings may be closed based on industry research on the likelihood of structural failures, but different studies may similarly reflect varying data. In conservation biology, animals are put on endangered species lists based on research on extinction risks, which are difficult to quantify. Psychiatrists operate similarly, having to digest general data about groups of patients and make judgments about medications, therapy, and commitment for individuals. These judgments are very often, but not always, informed by diagnoses and conclusions about patients’ functional abilities, which are in turn informed and defined by aggregate data from systematic studies or clinical experiences.
The law makes similar demands on the applied sciences. Indeed, in the courtroom, science is regularly employed to inform categorical decisions about individuals. As Faigman, Monahan, and Slobogin note, “reasoning from the group to an individual case presents considerable challenges and, simply put, is rarely a focus of the basic scientific enterprise. In the courtroom, it is the enterprise.” Was the eyewitness, who saw the perpetrator for a few seconds and who made a cross-racial identification of the defendant, accurate? Did the defendant’s toxic product cause the plaintiff’s illness? Is the defendant so intellectually disabled that he cannot be executed under the standards prescribed by the Eighth Amendment? The list of examples is nearly endless and has evoked a term of art to describe the dilemma of applying group data to individual instances, “the G2i problem.”
The challenges for a scientific expert in responding to these questions can be illustrated by considering the example of eyewitness identification. Studies of groups of people have demonstrated that—in addition to the problems that attend identification of suspects in general—cross-racial identification is particularly fraught with error. Most people, most of the time, are less adept at identifying persons of another race than identifying persons of their own race. But not every attempted identification of a person of a different race is inaccurate. The tendency to err—though demonstrable at the level of decisions made by many people trying to identify persons from other races—is not absolute. Many cross-racial identifications are, in fact, accurate. How then can an expert apply the group data that suggest a greater tendency toward error in cross-racial cases to the categorical determination that needs to be made in a particular case (i.e., whether this particular witness erred)? Even more to the point, should courts permit eyewitness experts to opine on the likely accuracy of a particular identification? And, if eyewitness experts are not given license to comment on particular applications of their data, why should any other expert be allowed to do so?
It is readily apparent that psychiatric testimony in court is subject to exactly this dilemma. As a discipline, psychiatry is oriented toward digesting large amounts of information for the purpose of categorizing individuals as falling within particular diagnoses, suffering certain conditions, or manifesting certain impairments. At the same time, however, the eyewitness example is also inapposite to the situation of psychiatry. Psychiatrists, unlike eyewitness researchers, customarily apply general research findings to particular cases. In that sense, psychiatry is more similar to other areas of medicine or even meteorology than it is to the typical research science.
Yet, the professional judgments involved in reasoning from the general to the individual case in ordinary psychiatric practice are not necessarily coterminous with the judgments required in court. Whereas psychiatrists assess individual patients for purposes of making individual treatment decisions, courts are interested in assessing the psychological characteristics of individuals to aid legal decisionmakers in dispensing fair and just outcomes pursuant to applicable law. For psychiatric testimony to aid in this process, psychiatric experts must apply to individual defendants or litigants data that are derived from the study of groups in a valid manner, and judges must understand the predicates for the appropriate use of such data. We suspect that often neither of these desiderata are met when psychiatric testimony is introduced. . . . Full Article.
Recommended Citation: Carl E. Fisher, David L. Faigman & Paul S. Appelbaum, Toward a Jurisprudence of Psychiatric Evidence: Examining the Challenges of Reasoning from Group Data in Psychiatry to Individual Decisions in the Law, 69 U. Miami L. Rev. 685 (2015).