Jury Decision Making Research

The jury has been one of the most mysterious forces in United States law. Critics have leveled extensive allegations that juries are unpredictable, unrepresentative of the population of the United States, biased, and irresponsible. Research into jury decision making has shed light on many phenomena in criminal and civil legal systems, but many questions remain.

Jury Decision Making ResearchJurors face an immensely complex task. What if a professor presented his or her class to students as though the students were jurors in a criminal trial? First, if students have prior knowledge of the course content or have taken the prerequisites, these students cannot register for the class. Second, students do not know how long the course will last or when the final examination will be scheduled. Third, students do not have just one instructor—they have two or more instructors who present radically different versions of the same events, and students, who are unfamiliar with the topic yet not allowed to research the material themselves, must decide which of these experts is correct. Fourth, students in this class cannot take notes or ask questions. Fifth, the final examination is a group project that requires all group members to agree unanimously on the response to a true or false (i.e., guilty or not guilty) question. Finally, based on the students’ answer to the question, someone will be released, incarcerated, or, as in some cases, sentenced to die. How many students would register for this class? Juries must manage a vast quantity of information and use this information in accordance with intricate instructions presented in complex legal jargon.

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One of the central and most controversial questions in jury decision-making research is how to conduct the research. A majority of this research has incorporated undergraduate students acting as mock jurors who read, hear, or watch a condensed trial. Legal and psychological scholars have long expressed concerns regarding the ecological validity of these findings (e.g., Konecni & Ebbesen, 1979). Bornstein’s (1999) extensive review of methods and outcomes, however, suggests that undergraduate jurors do not systematically differ from jury-eligible community members. In a series of meta-analyses of studies of jury decision-making research, Nietzel, McCarthy, and Kern (1999) reported that variables caused larger effects in controlled experiments with undergraduates and simplistic stimuli and that the effects of manipulated variables were smaller when research involved community-eligible mock jurors or realistic trial simulations. These and other concerns led them to advise jury researchers to seek convergent validity from four sources: (a) archival research of actual cases, (b) follow-up questions with actual jurors, (c) well-controlled simulations with mock jurors, and (d) realistic simulations with real juries or jury-eligible community members (Nietzel et al., 1999).

The composition of juries has raised questions about representativeness and fairness. Courts call jurors from voter registration lists and then seat juries from among the potential jurors who come to the courthouse. Not all United States citizens register to vote or are eligible to vote, and not all of the individuals who are called come to the courthouse. Judges disqualify some potential jurors due to conflicts of interest or other biases. Attorneys then use their own beliefs and sometimes the advice of psychologists acting as trial consultants to remove potentially biased jurors from the pool. Extensive disagreement exists in psychology and the law regarding the effectiveness of scientific jury selection. Selecting a jury based on personality traits of the jurors may generate small differences in trial outcomes, but for the defendant, whose life or liberty may be at stake, a small advantage may be worth the significant expense (Fulero & Penrod, 1990).

Although the strength of the evidence appears to be the most important factor in the outcome of a trial (Devine, Clayton, Dunford, Seying, & Pryce, 2001), numerous concerns exist that jurors’ decisions may be affected by extralegal (i.e., irrelevant) information. Jurors may be influenced by the defendant’s gender, wealth, race, or even attractiveness (Mazzella & Feingold, 1994). Legally irrelevant statements during the trial can also influence jury behavior. These statements could include evidence of the defendant’s prior conviction, other offenses with which the defendant is charged in the same trial, or inadmissible evidence that should have been excluded but was not (Nietzel et al., 1999). Although legal procedures such as judicial instructions exist to limit the impact of extralegal information, these instructions have little effect, and some researchers have found that these instructions increase the impact of the extralegal information (Nietzel et al., 1999).

Among other concerns regarding juries, scholars fear that expert witnesses can dominate juries and that jurors may not understand instructions. Judges act as gatekeepers and must decide whether an expert can present his or her views in a specific case. As dictated by Daubert v. Merrell Down Pharmaceuticals, Inc. in 1993, the judge must decide whether the expert’s claims have been tested, shown to be reliable, validated by peer review, and accepted by the scientific community. An extensive meta-analysis suggested that despite trepidations of undue influence of experts, juries appear to give moderate weight to expert testimony; experts are neither irrelevant nor overwhelming (Nietzel et al., 1999). Scholars also question whether jurors can sufficiently understand their task, particularly when following instructions written in legal jargon (Lieberman & Sales, 2000). Although researchers have demonstrated that rewriting jury instructions in simplified language can increase jurors’ comprehension (Lieberman & Sales, 2000), implementation of these changes in actual cases remains limited. Increasing acceptance of these findings will require continued endeavors on the part of psychologists and other scholars within and outside the legal system.

Difficulties in civil jury decision making include those described previously in this section as well as some additional challenges. In a typical civil case, the plaintiff sues the defendant for an injury, and jurors must decide whether the defendant is liable for the plaintiff’s injuries. If jurors find the defendant liable, they then assess monetary damages to be paid to the plaintiff by the defendant. Jurors’ tasks become particularly complex because their decisions of liability should be based only on the actions of the defendant but, if they find the defendant liable, the size of the damage award should be based only on the injuries of the plaintiff. Jurors, however, typically hear all of the information in a case before making decisions. The law requires that jurors use information about the defendant’s actions and ignore the information about the severity of the plaintiff’s injuries to decide liability and then use information about the degree of the injuries, but not the actions of the defendant, to decide damages. Jurors, contrary to legal expectations, use extralegal information about injuries to decide liability and use information about the defendant’s actions to decide damage awards (Greene & Bornstein, 2003).

If a defendant’s behavior is particularly malicious, jurors may award punitive damages to punish the defendant and to deter the defendant and others from engaging in such behavior in the future (Greene & Bornstein, 2003). The defendant’s wealth or ability to pay should also drive punitive damage awards. For punitive damages to meet these goals, they must be large enough to be significant to the defendant. Scholars of the legal system disagree regarding the possible influence of the severity of injuries in punitive damage awards, but in the 1996 case of BMW of North America, Inc. v. Gore, the U.S. Supreme Court addressed these conflicts and decided that punitive damages should have a reasonable relationship with the plaintiff’s actual or potential injuries (Robbennolt, 2002). Across all of these decisions, jurors receive little to no guidance regarding their damage awards (Greene & Bornstein, 2003). Future research will continue to explore the distinctions between legal expectations of jurors and jurors’ actual capabilities.

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