Application of Psychology to the Legal System

As we have noted, there are many opportunities for positive interaction between the fields of psychology and the law; however, this marriage of two disciplines does not come without some inherent conflict. Judges and attorneys are trained to look at human behavior in a way that is quite different from the perspective of psychologists. It is this difference that poses unique challenges for collaboration between the fields, though with an understanding of these differences, there is hope for a positive and appropriate partnership.

The Law is Based in Reason, Psychology in Empiricism

One of the difficulties in applying psychology to the legal field is the difference in the methods of decision making used by the two disciplines. More specifically, psychologists and legal players both strive for the same goal: to determine the truth, but the definition of “truth” and the methods used to uncover the truth differ. Psychology relies on principles and propositions that depend on confirmation by adhering to the scientific method—that is, testing hypotheses by appropriate methodology and appropriate observation. Psychologists generally seek an objective truth, seek to show consistent results over time, and rely less on intuition, or “gut feelings,” and more on scientifically based fact and probabilities (Carson, 2003). The law, on the other hand, relies heavily on legal precedent, or rulings in previous, similar cases, using these decisions as a guide for the current case. Similarly, the legal system is based on an adversarial system, which rests on the notion that the truth emerges from the clash of opposing parties in a courtroom. In other words, although each field may seek to answer the same question, psychology and the law utilize separate methodologies in determining what is “true” and how to determine that truth.

Guilty? Yes, No, or Maybe!?

Another difference between the two fields is the nature of the final outcome each discipline seeks. The legal field strives for absolutes—a defendant is guilty or not, competent or not, or mentally ill or not. A psychologist, on the other hand, is comfortable with a more relative position— that is, “it depends.” A psychologist deals in likelihood and statistical probabilities. A question often arises: “Does a psychologist’s role in helping to clarify these differences aid the legal system, or further muddy the waters?” After all, a psychologist’s most unequivocal statement is that a relation is “statistically significant,” which directly refers to probabilities, not absolutes.

For example, a forensic psychologist may testify that, according to empirical tests, 40 percent of eyewitness evidence is inaccurate. Should a particular witness’s testimony be categorized as falling within the 40 percent that is inaccurate, or within the 60 percent that is accurate? Further, is this split true and accurate under all conditions? Do the conditions and circumstances surrounding the situation matter (Clifford, 2003)? The psychologist has presented the findings in the best and most appropriate way the research may be interpreted, but the answer is most certainly not absolute. Consequently, a natural conflict appears when legal players call upon psychologists to help determine an absolute (i.e., is this witness accurate in her testimony?), especially when the psychologist answers in regard to likelihoods, or “maybes.” Lawyers and other legal professionals have difficulty with such gray answers, because legal cases generally require a black-and-white decision.

A Direct Conflict of the Law and Psychology: The Expert Witness

One of the roles a forensic psychologist may be asked to play, which may directly conflict with the law, is that of an expert witness (Ogloff, 1999). In this situation, questions of the level of knowledge necessary to be qualified as an expert, as well as the extent to which this expert opinion may lead to bias, are discussed. However, before a psychologist may be permitted to testify as an expert, it must be decided if the expert’s testimony meets the legal criteria to be held admissible. In the case of Daubert v. Merrell Dow Pharmaceuticals, Inc. (1993), the Supreme Court designated that judges’ decisions about the admissibility of expert testimony must turn on the validity of the science in question. In many respects, the judge acts as a gatekeeper, the one who decides if expert testimony may be admitted, according to the standards of science.

According to Daubert, there are several factors that must be considered in assessing the validity and admissibility of an expert’s testimony. First, the evidence must be relevant and reliable, according to four standards: (a) Is the theory or technique testable, and has it been tested? (b) Has the theory or technique been subjected to peer review or publication? (c) What are the reliability and the error rate for the scientific technique? (d) Is the theory generally accepted in the scientific community? In short, the parameters of expert testimony make clear that only information that is relevant to the case, and necessary to the trier of fact, will be considered admissible by a judge. It is the job of the expert witness to be sure this scientific testimony is expressed in an accurate, honest, and clear manner to the court. Sometimes this must occur when it is not necessarily in the best interest of one of the opposing sides to do so.