The science of psychology exists in a state of tension with the legal system in many ways (Ogloff & Finkelman, 1999). Fundamentally, the goals and processes of investigation in science differ substantially from those of investigation in the law. First, science is inductive. Researchers examine data from many field studies, correlational studies, and experiments and draw tentative, probabilistic conclusions. The law wants an answer that is, at least in criminal law, beyond a reasonable doubt.
Second, scientific conclusions remain provisional and open to falsification, and conclusions change in light of new data, new methodologies, and new paradigms. Court decisions set precedents that remain resistant to change without consideration from state or federal supreme courts. In other words, science cannot provide certainty of conclusions for the future, but the law looks to past legal precedents to determine truth and direct future policy.
Third, psychological science is nomothetic instead of ideographic. Researchers attempt to describe, predict, and explain the behavior of populations of organisms across a wide range of contexts in terms of probability—a researcher cannot predict the behavior of any particular individual with 100 percent accuracy. In contrast, judges and juries must evaluate the actions, intentions, accuracy, and other characteristics of each individual involved in a particular case. For example, researchers may predict that a population of highly confident eyewitnesses (i.e., those who are 95 percent certain of their memories) will make errors in approximately 15 to 30 percent of their claims (Wells, Memon, & Penrod, 2006), but researchers cannot determine whether a particular statement by a particular eyewitness is correct. The law, however, must evaluate the truthfulness of each statement by each eyewitness.
Fourth, a courtroom brings together two opposing sides who argue for competing views of truth. A community of scientists conducts a wide variety of research endeavors and then tries to form one general view of a psychological topic. Although researchers may report conflicting findings and may challenge one another about methods, outcomes, or interpretations of research, science seeks to improve the general body of knowledge. However, science does not determine truth by having two adversaries challenge each other (Ogloff & Finkelman, 1999).
Methodology in psychology and the law is as broad as the field itself. Some researchers observe behavior in natural settings or search archival data for existing trends in actual court cases. For example, in civil jury research, Chin and Peterson (1985) found evidence for the deep pockets hypothesis, the notion that wealthier corporate or government defendants are more likely to be found liable and to pay larger damages than are less wealthy individual defendants, but wealth and corporate identity remain confounded in the archival data.
These approaches yield ecologically valid data, but they lack experimental control. Other researchers use correlational data to assess policies or other phenomena even though this approach does not allow them to make causal inferences. For example, scholars use correlational methods to study the predictive validity of eyewitness confidence for eyewitness accuracy (Wells et al., 2006). Still other researchers may run well-controlled experimental simulations of legal events.
These psychologists may ask participants to act as witnesses to staged events, videotaped crimes, or written descriptions of crimes, or they may ask participants to play the roles of jurors, interrogators, or even suspects (e.g., Kassin & Fong, 1999). Sometimes lines of research converge, as they do in the false confession literature, and in some cases different methodologies yield different results. For example, MacCoun’s (1996) well-controlled experimental investigation of the deep pockets hypothesis revealed that corporate identity is more important than wealth in civil suits. Wealth and corporate status were confounded in the archival data, but when MacCoun (1996) separated these variables experimentally, the participant-jurors were more likely to find corporate defendants than individual defendants liable across levels of income. The diversity of the field and the wide variety of goals of research result in a broad range of available methods for researchers to choose.
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