Under the Federal Rules of Evidence and virtually all state codes, expertise is defined by the nature and scope of the proffered opinion. The basic issue with regard to a qualifications assessment is whether the witness has the background to support his or her intended testimony. An expert must be qualified to “assist the trier of fact.” But no strict tests or minimum requirements apply to the assessment of qualified expertise. The level of qualifications required varies with the demands of the proffered testimony.
The Federal Rules of Evidence, for example, define qualifications broadly, encompassing “knowledge, skill, experience, training, or education.” In general, courts interpret the main qualifications requirement in relation to the expert’s claimed expertise and the nature of the testimony. Hence, experts on medical matters are expected to have medical degrees, appropriate certifications, and experience, but auto mechanics or real estate appraisers might only need years of experience and demonstrable skills. Professional degrees or certifications, therefore, may be considered by courts because they reflect the expert’s level of skill or experience but are not formal requirements of the rules. As a practical matter, courts typically consult the experts’ respective fields for guidance regarding what constitutes a “qualified” expert. Not all fields, however, have well-articulated standards, and many subjects of interest to the law are studied by fields with widely varying professional requirements.
Because an expert’s qualifications must be sufficient to support his or her intended testimony, courts regularly demand that experts possess certain minimal degree requirements or professional certifications before being allowed to testify. In a case presenting an issue of medical causation, for instance, a court is likely to require an expert to possess a medical degree. Similarly, testimony regarding structural engineering will typically be introduced through the testimony of a structural engineer. In most jurisdictions, the question of a particular expert’s qualifications is within the discretion of the trial court and will not be overturned absent a finding that the lower court abused its discretion. Indeed, it is highly unusual for an appellate court to reverse a lower court’s finding that a particular expert passes or fails the qualifications test.
With regard to fields with highly formalized credentialing requirements, courts tend to follow the respective field’s expectations regarding what it takes to be “qualified.” This usually means that the courts mirror the respective fields from which the experts hail. If, for example, a field requires certification to practice the expertise, courts tend to assume that party experts from that field will possess the requisite certification. Experts who fail to meet their own field’s qualifications demands are presumed unqualified by most courts. This, however, is a rebuttable presumption. Courts use a field’s certification requirements as a guidepost for judging expertise, not as a prerequisite to receiving an expert’s opinion. In effect, therefore, a field’s certification requirement constitutes a factor, albeit an important one, in the assessment of qualifications.
Many expert fields, however, have no formal credential requirements, and the courts similarly follow the field’s lead here too. Hence, medical experts usually must have attained the M.D. degree at a minimum, but experts on psychological subjects might possess a host of degrees or even experience-based specialization. For example, courts sometimes find experts with just a B.A. degree, together with significant work experience, to be minimally qualified to testify generally on subjects such as the battered woman syndrome or child abuse accommodation syndrome.
Although courts are typically permissive regarding credentials when experts propose to testify on general subjects in psychology, there are limits to this generosity. In particular, courts might require higher educational attainment before an expert will be permitted to testify about a relevant diagnosis. For example, while a court might permit a social worker with relevant experience to testify that it is not unusual for rape victims to fail to immediately report an assault, it is likely to require clinical certification to diagnose the alleged victim as suffering from posttraumatic stress disorder. Similarly, courts usually demand a medical degree to support testimony about drug treatment or the effects of a particular drug regime on human behavior.
Perhaps the most pressing issue presented in the context of expert testimony is whether experts must demonstrate specialized knowledge of the subject of the testimony. The hallmark of contemporary science (and all expertise) is specialization. This trend leaves courts somewhat uncertain as to whether generalists should be permitted to testify about matters that are highly specialized. Courts tend to approach this matter flexibly. In practice, this means that the matter is within the trial court’s discretion. Some courts require experts to have demonstrated expertise in the specific areas and topics on which they are to testify. Other courts provide that generalists may testify on specialty areas and that their lack of expertise in those areas is a matter of weight for the trier of fact.
All the general issues presented regarding the qualifications of experts to testify can be found in the many legal contexts in which training and experience in psychology might assist triers of fact. Indeed, psychology possibly illustrates better than any other field the complexities associated with measuring an expert’s qualifications. Psychological expertise comes in myriad forms and is introduced for a great variety of purposes. As a general matter, as is true with other areas of substantive expertise, an expert psychologist’s qualifications depend on the nature of his or her proffered testimony. A witness proposing to testify on the unreliability of eyewitnesses, for example, would be expected to be steeped in the research in this area. A witness proffered on whether a defendant suffered from posttraumatic stress disorder would be expected to have clinical expertise. These two examples roughly represent the two basic domains in which psychologists are offered to testify: research-based knowledge and clinical opinion. Each of these domains presents special difficulties with regard to qualifications, not least because there is no obvious line that divides the two.
In a number of legal contexts, psychological research is relevant to general background facts, even if the expert cannot reliably testify regarding how those circumstances affected the particular case. Specifically, research studies can often assist the trier of fact to understand the background context regarding some matter that is relevant to the case at hand. For example, researchers might offer to testify regarding the suggestibility of young children to leading questions in a case involving sexual assault, but they may be unable to provide a reliable opinion regarding whether a particular child’s testimony was influenced by the questioning that occurred in the case at hand. A witness proposing to testify regarding general research results should generally have expertise in the relevant literature as well as in statistics and research design. Very often, an expert proffered to testify regarding a particular research area will be someone who has published extensively on the subject—though this would not be a prerequisite in most jurisdictions.
In many cases, expert psychological evidence will also be proffered on an issue that is particular to the case. In theory, the proponent of such testimony has the obligation to demonstrate the admissibility of both the general framework and the framework’s applicability to the particular case. With regard to expert qualifications, at least in theory, this means that an expert must be qualified on the research basis for the general framework and the clinical application of that research framework to particular cases. This will often mean that different experts will testify to these two subjects. Consider, for example, a defendant who claims that she killed in self-defense based in part on the battered woman syndrome. As an initial matter, the defendant has the burden to demonstrate the basic validity of the claimed syndrome. This is a claim that ought to be premised on the research literature and should be introduced by an expert qualified to discuss the strengths and weaknesses of that literature. Additionally, the defendant is likely to proffer an expert opinion that she suffered from the syndrome. This very often requires the introduction of an additional expert, one qualified to offer clinical expert testimony that is relevant and reliable for the particular claim.
It must be emphasized that the issue of qualifications is intrinsically bound to the associated standards for admissibility of the substantive expert testimony. In federal cases, for example, this means that the admissibility inquiry will be parallel to the determination made under Rule 702 and Daubert v. Merrell Dow Pharmaceuticals (1993) and its progeny. Accordingly, if an asserted expertise cannot be shown to be sound, then even the most eminent (most highly qualified) practitioner of that asserted expertise still would not be permitted to testify as an expert. In fact, courts are likely to find that the issues of qualifications, reliability, and fit are inextricably intertwined and, in practice, cannot easily be disentangled. Qualifications are relative, being more or less useful depending on the expert’s familiarity with the subject that fits, or is relevant to, the matter to be decided by the trier of fact. Qualifications, therefore, cannot be evaluated in the abstract. At some point, certainly, the question of qualifications becomes a matter of weight rather than admissibility. But just as with Rule 702 validity assessments, the judge’s gatekeeping obligations should extend not merely to qualifications in the abstract but qualifications to testify about the subject that is relevant to the issues in dispute.
- Berger, M. (2002). The Supreme Court’s trilogy on the admissibility of expert testimony. In Federal Judicial Center (Ed.), Scientific evidence reference manual (2nd ed., pp. 9-38). Washington, DC: Federal Judicial Center.
- Daubert v. Merrell Dow Pharmaceuticals, 509 U.S. 579 (1993).
- Faigman, D. L., Kaye, D. H., Saks, M. J., Sanders, J., & Cheng, E. K. (2007). Modern scientific evidence: The law and science of expert testimony (2nd ed.). St. Paul, MN: West/Thompson.
- Giannelli, P. C. (2004). Expert qualifications: Who are these guys? Criminal Justice, 19, 70-71.
- Murphy, C. P. (1994). Experts, liars, and guns for hire: A different perspective on the qualifications of technical expert witnesses. Indiana Law Journal, 69, 637-657.