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The previous column was the first part of a discussion of the applicability of Daubert v. Merrell Dow Pharmaceuticals Inc., 509 U.S. 579 (1993), to “soft” sciences such as mental health expertise. Prior to Daubert, there were two leading schools of thought about the admissibility of such testimony. Some questioned whether such testimony should be admissible at all. The proponents of this view argued that the reliability of mental health testimony pales in comparison to the trustworthiness of the testimony based on disciplines such as physics. Judge Bazelon thought out loud that diagnostic criteria in psychiatry were so soft that psychiatric testimony was of little value to the trier of fact. Washington v. U.S., 390 F.2d 444 (D.C. Cir. 1967). Even in ‘hard’ sciences, no absolute certainty At the other extreme, some contended that soft scientific testimony ought to be routinely admitted with little scrutiny. Particularly in jurisdictions adhering to the Frye test, the tendency was to limit the scope of the test to instrumental scientific testimony such as the polygraph. The advocates of this view reasoned that only testimony about the proverbial “black box” poses an acute risk that the lay jurors will overvalue the testimony. People v. McDonald, 690 P.2d 709 (Calif. 1991). In Daubert jurisdictions, though, most courts have rejected both extreme views. In Daubert, Justice Harry Blackmun acknowledged that even in the “hard” sciences, experts cannot attain absolute certainty. 509 U.S. at 590. In that light, the hard and soft sciences differ in degree rather than kind. The justice announced a broad definition of science expansive enough to encompass soft science. Moreover, in Kumho Tire Co. v. Carmichael, 526 U.S. 137 (1999), the court ruled that the proponent of any type of purportedly expert testimony must demonstrate its reliability. Yet, propositions in soft science obviously cannot be validated in the same manner or with the same precision as hypotheses in the harder sciences. If a toxicologist hypothesizes the reliability of a new intoxication testing technique, he or she can validate the hypothesis by comparing readings yielded by the new test to readings in direct blood alcohol tests. A psychiatrist cannot validate an hypothesis about a new syndrome in the same fashion. However, in a soft science, researchers can make a good-faith effort at empirical validation. Faigman, “To Have and Have Not: Assessing the Value of Social Science to the Law as Science and Policy,” 38 Emory L.J. 1005 (1989). Suppose that in a premises liability action, the plaintiff alleges that while she was a guest at a hotel, she was raped. To prove the occurrence of the rape, the plaintiff not only testifies about the event; she also calls a psychologist to corroborate her testimony. The psychologist is an experienced rape counselor. He has worked in that capacity for 20 years and, during that time, he has developed a profile of the rape victims who have visited the center. In his judgment, the plaintiff’s background and conduct match that profile. Based on that match, he opines that the plaintiff was certainly subjected to a rape. It is submitted that Daubert and Kumho would require the plaintiff to lay the following foundation for that opinion. The expert is relying on a comparison between the plaintiff’s background and that of the alleged victims included in the center’s database. The proponent must show that: There is some extrinsic, independent corroboration that the women included in the database were in fact raped; that one or some of those women displayed a certain set of symptoms-the symptoms in the profile the plaintiff matches; and that no one who is not a rape victim displays that set of symptoms. The plaintiff proposes using the expert’s testimony as substantive evidence of a rape. The plaintiff must validate the center’s database as a fact-finding tool. State v. Saldana, 324 N.W.2d 227, 230 (Minn. 1982). Although the expert cannot establish that with a gas chromatograph mass spectrometer, the expert can make a good-faith effort to substantiate the truth of the reports of the women included in the database. It would be unscientific to uncritically accept the reports at face value. The expert can follow up by contacting emergency rooms to learn whether the women displayed physical evidence of assault, police departments to determine whether suspects confessed to the rapes, and prosecutors’ offices to learn whether there were convictions in ensuing prosecutions. Even if the expert made such a bona fide effort, that effort might still yield an inadequate foundation for the opinion. This expert contemplates using the adverb, “certainly.” Logically, that opinion is unsupportable unless the proponent can lay the second and third foundational elements. The third element is critical. That element establishes the specificity of the profile: The profile is displayed only by women who have been raped. The opinion cannot be couched in absolute terms if other types of stressors can produce the symptoms which comprise the profile. Alternatively, assume that the expert is prepared to testify to the more limited opinion that the plaintiff was probably raped. In the first variation, the underlying hypothesis was that there is a set of diagnostic criteria that enables an expert to determine with certainty whether a victim was raped. In this variation, the expert is no longer relying on that hypothesis. Since the hypothesis changes, the foundation differs. In one respect, the foundation is the same. In both cases, the plaintiff wants to use the expert’s testimony as substantive evidence. For that reason, in both cases the expert must demonstrate that there has been some empirical substantiation of the truth of the reports included in the database. However, the required findings differ. In this variation, the opinion is admissible if most rape victims display the profile but most persons who are not rape victims do not. Unless the data support both findings, it is illogical to infer that the plaintiff “probably” was raped because she matches the profile. Vary the hypothetical again. Now the expert is going to venture an even more circumscribed opinion: The fact that the plaintiff matches the profile is “some evidence” or “consistent with the hypothesis” that she was raped. The proponent is putting the expert’s testimony to a substantive use. Consequently, as in the previous variations, the proponent’s expert must have endeavored to validate the truth of the reports of the women included in the database. However, since the ultimate opinion changes, the other foundational elements change. Now the only required findings are that the women included in the database display the symptoms more frequently than women who have not been raped. It is unnecessary for the proponent to show that a majority of the women in the database fit the profile. Assume, for example, that while 20% of the women in the database fit the profile, only 10% of the general female population does. That contrast supports the expert’s opinion. But note that without a baseline frequency for the general population, it would also be insufficient to show that a majority of the women in the database fit the profile. Suppose that an expert opined about child sexual abuse accommodation syndrome (CSAAS) testified only that 55% of the children of a certain age who had supposedly been abused displayed bed wetting. If 60% of the children of that age in the general population display the symptom, that symptom is not probative that the children in the database were abused. Commonwealth v. Dunkle, 602 A.2d 830, 832 (Pa. 1992) (“the very same behaviors” exhibited by children who have not been abused). A baseline frequency is necessary. Take the analysis with a teaspoon of salt, not a grain Vary the hypothetical one last time. Suppose that in the premises liability case, the plaintiff delayed reporting the offense to the police. At trial, the defense treats the delay as impeaching evidence. The plaintiff calls the same expert to rehabilitate the plaintiff’s credibility. The plaintiff claims that her prior conduct is not inconsistent with her rape claim. The expert will testify that many of the women in the center’s database similarly delayed calling the police. In this variation, the proponent is offering the testimony merely as credibility evidence The expert does not need to empirically validate the reports included in the database. The expert testifies that the women who displayed that symptom received the sort of medical treatment and psychological counseling appropriate for rape victims and the mental health of most of those women improved. Of course, some of the women could have been lying. Yet, proof of a large number of successful, clinical interventions strongly suggests that the majority were being truthful. If logic supports that inference, the foundation is adequate to justify admitting the testimony as credibility evidence. People v. Bledsoe, 681 P.2d 291 (Calif. 1984); People v. Hampton, 746 P.2d 947 (Colo. 1987). Take the above analysis not with a grain of salt but rather with an entire teaspoon. The lower courts are just now beginning to struggle with the extension of Daubert to soft science. However, even at this early point in the evolution of the case law, some generalizations seem reasonably clear. Whenever the proponent proffers soft scientific expertise as substantive evidence, the proponent’s expert must endeavor to empirically validate his or her underlying theory. The expert cannot employ the instrumental validation methodologies used in the hard sciences, but the expert has to make a good-faith effort to adapt empirical techniques. In ruling on the sufficiency of the proponent’s foundation, the trial judge ought to fall back on the normal rules of logic. The more definite the expert’s final opinion-”certainly” rather than “probably” or “probably” rather than “some evidence”-the more demanding the trial judge should be. Edward J. Imwinkelried is the Edward L. Barrett Jr. professor of law at the University of California, Davis. He can be reached at [email protected].

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