Jury Trials Research Paper

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Public praise and criticism for the jury have a long history, and high profile jury trials are a staple of modern press coverage. However, it is only in the past forty years that researchers have published systematic empirical studies of jury behavior. Study of the jury is a particularly thorny project because the jury speaks publicly only through its verdict. At the end of the trial the jury retires to deliberate in the privacy of the jury room. It emerges occasionally to ask a question, but more commonly, only to report its verdict.

The jury in the United States gives no explanation for its verdict and the jurors can return to their pretrial lives without revealing any information about how they arrived at their decisions. Research on the jury, as a result, has relied on a variety of indirect methods, each with strengths and limitations: (1) archival studies of jury case characteristics and verdict patterns (records provide information on large samples of cases, but courts record a limited number of variables); (2) post-trial interviews with jurors (the jurors are reporting on the actual process of reaching a verdict, but what they report is limited to what jurors noticed, accurately recorded, remember, and are willing and able to report); (3) surveys of other trial participants, such as judges and attorneys (these respondents are informed court observers, but they have only indirect information on jury behavior and their reports may be influenced by the verdict); (4) field experiments (these can offer strong evidence on the impact of a legal reform like juror note-taking, but they provide little information on process and are hard to implement successfully); and the most common approach; (5) simulation experiments (simulations are strong on process information and provide unambiguous causal inference, but generalizability of findings depends on correspondence with dynamics of real jury behavior). By combining these various approaches, researchers have compiled a nuanced, although incomplete, picture of jury behavior.

The Role of The Jury in The Criminal Justice System

Most criminal cases, even in the United States, end in dismissals or guilty pleas. In addition, if the case does go to trial and the defendant does not exercise the right to a jury trial, it will be decided by a judge. An estimated 150,000 jury trials occur in state courts and an additional 10,000 (half of them criminal trials) in federal courts. Yet the influence of the jury extends far beyond the trials it actually decides. The terms of a plea agreement and the decision to let a judge decide the case are based on what attorneys and defendants anticipate would happen if the case were decided by a jury.

The jury also plays a political role in the criminal justice system. In addition to deciding cases, the jury is a potential source of legitimacy for the legal system. To the extent that the jury is viewed as representing a fair cross-section of the community, its verdict is likely to be seen as the product of fair consideration and can carry a legitimacy that the decision of the judge, as an employee of the state, may lack. Even when the jury’s verdict is unpopular, and even if observers believe that the jury does not fairly represent the community, the jury acts as a lightning rod, insulating the judge and other parts of the state legal system from criticism.

The jury also can act as a conduit for community standards. For example, in evaluating a claim of self-defense, the jury must determine what a reasonable person would be expected to believe, as well as what the particular defendant did believe. Although the jury is charged with applying the law it receives from the judge to the facts, this example illustrates the fuzziness of the division between law and facts. The jury must often inject its understanding of appropriate standards into its fact-finding even while scrupulously following the instructions that the judge provides.

A final political role for the jury is its educative function, identified by Alexis de Toqueville as the jury’s great strength. Surveys suggest that more than one-half of American adults have had some personal involvement with the courts; of this sub-group, half have served on a jury. Citizens also receive information and misinformation on the courts from other sources, including the media. The extent to which jury service provides additional or corrective information is unclear, but jury experience tends to make jurors feel more positive about the jury system.

Judge Versus Jury

One way to evaluate jury behavior is to compare the decisions reached by juries with those reached by judges. Studies of judge-jury agreement reveal substantial, but not uniform agreement. In Kalven and Zeisel’s classic study of jury trials, judges reported the jury verdicts for each of the jury trials over which they presided. They also indicated how they would have decided the cases if they had been bench trials. In 78 percent of the cases, the judge and jury agreed on the verdict. In disagreement cases, the judge would have convicted when the jury acquitted in 19 percent of the cases and the jury convicted when the judge would have acquitted in 3 percent of the cases, a net leniency of 16 percent.

When disagreement arose, it was not attributable to case complexity. Cases that the judge rated as high in complexity were no more likely to stimulate disagreement between the judge and jury than were cases that were low in complexity. The disagreements emerged most often (in 45 percent of the disagreement cases) from the combination of a difference in interpretation of the evidence (the jury’s traditional fact-finding role) and an issue of values (e.g., the jury’s preference for an expanded version of the law of selfdefense). Different conclusions about the facts alone accounted for 34 percent of the disagreements, and values alone accounted for only 21 percent of the disagreements.

Kalven and Zeisel collected their data in the late 1950s, but despite many changes in the makeup of the jury pool and the bench, a very similar pattern was found more recently by Heuer and Penrod. In a sample of criminal trials, they obtained a rate of 74 percent agreement, with the judge convicting when the jury would have acquitted in 23 percent of the cases and the jury convicting when the judge would have acquitted in 3 percent of the cases, a net leniency of 20 percent.

A few researchers have examined the impact extra-legal factors, such as inadmissible evidence, or judicial decisions. The results suggest that judges as well as jurors are susceptible to cognitive biases that can influence their verdicts.

How Jurors Evaluate Evidence

The traditional legal model of the jury trial portrays jurors as passive recipients of the evidence and legal instructions. However, empirical studies of jury behavior find jurors to be active processors of incoming information. Early models of jury decision-making included (1) ‘‘averaging models,’’ in which jurors assess and weigh each piece of evidence, combining the results to reach a verdict and (2) ‘‘Bayesian models,’’ in which jurors consider and evaluate each new piece of information, revising their position on the appropriate verdict in light of their prior position and the additional evidence. These formal models have enjoyed limited success as descriptions of how jurors actually decide cases.

Explanation-based models of jury decisionmaking, such as Pennington and Hastie’s story model, provide an account of jury behavior that comports better with empirical evidence about jury behavior. Consistent with the story model, jurors do not simply record and store the evidence for later use as they receive it. Rather, they actively select and organize the trial evidence to construct a story about what happened. The story they construct is based on the evidence, but jurors also use it to fill in gaps in the evidence by drawing inferences based on their understandings of how the world works. Jurors arrange evidence in the form of a sequence of motivated human actions that include important events, the circumstances of the case, inferences about character, and the parties’ motivations and states of mind. By influencing jurors’ understanding of what took place, the order in which facts are presented (i.e., in story order rather than witness order) can affect verdicts. No studies have investigated whether the story model provides a reasonable account of decision-making by judges as well as jurors.

Jury Composition

The modern American jury is far more heterogeneous and representative of the citizenry at large than was the early English jury or even the American jury in the early twentieth century. Nonetheless, the jury is not a random sample of citizens. It is the product of a multi-stage selection process that typically begins with a list of potentially eligible jurors drawn from voter registration lists and often supplemented by lists of individuals holding drivers’ licenses in the general geographic area where the court sits. Prospective jurors may be excused from jury service on the basis of hardship, but losses also arise as a result of geographic mobility, a failure to update the lists, and nonresponse by prospective jurors to a court summons. The loss of prospective jurors in the qualification and summons process results in a systematic underrepresentation of minorities, younger individuals, and those at lower income levels.

The final stage in jury selection occurs when prospective jurors are brought into the courtroom and questioned to determine whether they will serve in the particular case. Those who clearly express preconceived notions about what the verdict in the case should be, and those with clear conflicts of interest, are excused by the judge (the challenge for cause). In addition, the parties can excuse a limited number of prospective jurors without giving a reason (the peremptory challenge). The U.S. Supreme Court has ruled— Batson v. Kentucky, 476 U.S. 79 (1986); J.E.B. v. Alabama ex rel. T.B., 511 U.S. 127 (1994)—that peremptory challenges based on race or gender are constitutionally prohibited, but that prohibition fails to eliminate racially and gender motivated challenges because courts generally require the party making the challenge to provide only minimal justification when the opposing party charges that a challenge was improperly motivated. Also, given the small number of jurors challenged in the typical trial, an attorney can generally identify a unique and nondiscriminatory reason for each challenge.

The result of this variety of shaping and sometimes cross-cutting forces is that juries tend to be somewhat more educated, wealthier and older, and less likely to include a representative number of minorities, as compared to the distribution of these groups in the adult population. Although these differences are likely to persist, the American jury today is more representative than ever before, and is more heterogeneous than the juries of other countries with a jury system. Moreover, jury participation is extensive. Surveys indicate that 25 percent of American citizens are likely to serve on a jury trial at some point in their lives.

Individual Differences

Attempts to predict juror verdict preferences based upon juror’s background characteristics have had limited success. For example, demographic characteristics like gender, race, and age generally account for very little of the variation in jurors’ responses. Attitudinal characteristics can be more powerful, albeit also modest, predictors.

Expectations, beliefs, and values affect the way jurors react to evidence. In that respect, jurors are no different from any other decisionmakers, because people ordinarily scrutinize more carefully, and are more likely to reject, information that is inconsistent with their beliefs and expectations. It is generally easier for people to remember theory-consistent information than theory-inconsistent information; moreover, ambiguous information tends to be interpreted as theory-consistent.

Some types of legal cases and issues are more likely than others to implicate strongly held beliefs or values. A primary example concerns the death penalty: even among jurors willing to impose the death penalty in some cases, the strength of their support for the death penalty can strongly influence the likelihood that they will vote for a death sentence.

Pretrial Publicity

The American constitutional right to a free press occasionally provides the public with information or misinformation about the case that a jury will be asked to decide. Under such circumstances, the constitutional rights to a free press and to a fair trial are potentially at odds. This conflict is not faced in countries like Canada and Great Britain where the press is prohibited from writing about impending trials. For example, pretrial publicity about a defendant’s alleged confession can affect the expectations and beliefs of prospective jurors in the United States. Although some limited research indicates that the effects of some types of pretrial publicity are generally small, it also suggests that jury selection and the passage of time may not eliminate them. In some high-profile cases, the legal system faces not only the cost of moving a trial, but also the increasing difficulty of identifying a location that has not been saturated with pretrial media coverage.

The Jury’s Response to Experts

Trials increasingly involve the testimony of experts who present technical and scientific evidence. The addition of DNA evidence to the usual range of forensic testimony is a prime example. Surveys of jurors indicate that they find expert testimony to be useful, but they are wary of experts and their potential biases, a factor that can affect an expert’s persuasiveness. Jurors typically work hard at trying to understand the content of expert testimony. Motivation, however, is not enough to ensure success and jurors often express concern about their ability to handle complex evidence.

Jurors are instructed to base their verdicts on the evidence presented at trial and legal instructions. However, their ability to fully process the evidence may be reduced if the expert fails to teach as well as attempt to persuade. When faced with technical testimony, jurors look for cues about the trustworthiness of the source, sometimes using the language itself as a cue. When a decision-maker accepts a persuasive message in response merely to cues (e.g., the prestigious credentials or complicated language of the source of the message), and has not processed and evaluated the message itself, the decision-maker is engaging in peripheral (or heuristic) processing. This approach contrasts with the central (or systematic) processing of the expert testimony that occurs if there is a thorough evaluation of the evidence.

There is little evidence to suggest that jurors adopt the position of an expert based solely on peripheral cues. What is more likely to happen is that the juror will reject unintelligible expert testimony. Moreover, unintelligible jargon may lead jurors to give less credence to an expert who displays other evidence of potential bias, such as an unusually high rate of pay.

Jury Size and Decision Rule

Traditional English and American juries consisted of twelve members who were required to reach a unanimous verdict. Some American jurisdictions now permit juries with as few as six members and nonunanimous verdicts of 9–3 or 10–2; England permits a 10–2 verdict if the jury has been unable to reach unanimity within a specified period of time. Reducing jury size increases the likelihood of an aberrant jury verdict. A majority-decision rule tends to reduce the rate of hung juries and to shorten deliberations because jurors in the majority do not need to gain the support of all jury members. It may also result in less thorough deliberations if the deliberators can arrive at a verdict without considering the reasons why there is disagreement among the members of the jury.

Reactions to The Law, Including Nullification

In theory, jurors are expected to apply the law to the facts of the case. However, a verdict rarely reveals whether the jury has applied the judge’s legal instructions, or whether the jury has applied the judge’s instructions accurately. Thus, trial and appellate courts are left to assume that the jury has followed the judge’s instructions when the verdict is consistent with the law under at least one possible interpretation of the facts. Questions about the jury’s use of the legal instructions typically arise at the appellate level only in the context of concerns about whether the trial court has stated the legal standard accurately. If the statement of the law comports with the legal standard, questions are rarely raised regarding whether the judge conveyed the standard clearly enough to be correctly applied.

Jurors might fail to follow the judge’s instructions on the law if they were either unmotivated or unable to apply the instructions. Empirical studies of the jury show that jurors see themselves as obligated to apply the law, and that they spend a significant portion of their time during deliberations discussing the law. Yet, there is also evidence that legal instructions as they are typically given often fail to provide jurors with helpful legal guidance. Nearly twenty years ago, Elwork, Sales, and Alfini examined juror comprehension of several frequently used jury instructions. They showed not only that comprehension was low, but also that it could be significantly improved if the instructions were rewritten using a combination of psycholinguistic tools and common sense.

More recent work has demonstrated additional ways to facilitate comprehension. The traditional approach to jury instructions is to tell the jury only what it is supposed to do, and to avoid directing attention to any matter that the jury should ignore. But failing to address the erroneous beliefs that jurors do have does not make those beliefs go away, and it does not neutralize them. For example, if jurors are worried about whether a defendant not sentenced to death will be eligible for parole, avoiding any mention of the parole issue during jury instructions can leave jurors believing that a swift release is likely. Jurors come to court with expectations, beliefs, and schemas that can powerfully affect perceptions, attention, and recall. When instructions fail to correct inaccurate legal impressions, they miss the opportunity to provide jurors with a meaningful legal framework.

Although the most common source of deviations from legal standards is a failure of the legal instructions to convey clearly what the appropriate legal standard is, jurors also may deviate from the path outlined in the instructions due to cognitive biases or motivational obstacles. Jurors admonished to disregard particular information may find it difficult to do so. Other legal instructions may ask the jurors to engage in mental gymnastics that are not easy to perform, for example, to use a defendant’s criminal record only to assist in evaluating his credibility, but not as evidence of bad character; to forget that they learned about damaging evidence that the judge ruled inadmissible. Yet, jurors may be unwilling or unable to perform the required cognitive adjustments. A series of simulation experiments have illustrated that such inadmissible evidence can affect juror decisions. The remaining question is whether these failures are significantly less likely when the trier of fact is a judge, or whether they represent heuristic patterns of using information that neither a judge nor jury can overcome.

Finally, jurors may depart from the judge’s legal instructions when the application of the legal standard to the particular case so substantially violates the jurors’ sense of justice that they are persuaded to temper the letter of the law. This conduct has come to be known as ‘‘jury nullification.’’ Kalven and Zeisel attributed most of the disagreements they found between judge and jury to evidentiary disputes, reporting that the jury is engaged in only a modest rewriting of the law in cases that are close on the evidence. Yet, even if it is rare, explicit jury nullification of the law plays a central role in conceptions of the jury and has been a source of extensive debate. Although courts have long recognized the power (as opposed to the right) of the jury to nullify, courts and commentators have disagreed about whether juries should be told about that power (United States v. Dougherty, 472 F.2d (D.C. Cir. 1972); United States v. Thomas, 116 F.3d 606 (2d Cir. 1997)). Empirical research indicates that the distinction between the power and the right matters: when jurors are explicitly instructed that they have the right not to apply the law as the judge describes it, they are more willing to reach verdicts that temper the literal application of the law.


Deliberations resulting in a group verdict distinguish the jury from its chief alternative, the trial court judge, in two ways. First, the jury verdict in principle reduces the likelihood that the decision will represent an idiosyncratic view of a single deviant decision-maker. Second, in theory, deliberations give the jury an opportunity to profit from the resources of its multiple members and to pool its knowledge and sensibilities to resolve differences. Presumably, a jury verdict reflects more than what could be achieved either by a single decision-maker or by mechanically combining or averaging the preferences of the individual members.

The extent to which deliberations actually do affect jury verdicts in criminal cases is in dispute. Some scholars have suggested that jury verdicts simply reflect the position of the majority before deliberations begin. This suggestion is consistent with the verdict-driven jury that takes an immediate vote to see where each juror stands and then focuses its attention on persuading the minority to join the position initially held by a majority of the jurors. When a vote is immediate, it is likely to reflect predeliberation preferences. When a discussion of the evidence precedes a vote (the so-called evidence-driven jury), that vote will be affected by any changes that have occurred as a result of the discussion. Although jurors often call for an immediate vote, discussions can interrupt before a vote is completed, so that first votes often are not immediate and they imperfectly reflect the individual predeliberation preferences of the jurors. Nonetheless, most juries probably do end up reaching a verdict that reflects the majority position that was apparent at the time most of the jurors expressed a verdict preference in deliberations. The majority, using both normative and informational pressure, persuades the minority to accept its position. When the jury in a criminal case is evenly divided on its first vote, some evidence suggests that the ‘‘beyond a reasonable doubt’’ standard will make a not guilty verdict more likely than a guilty verdict.

Reforming Jury Trials

The jury is regularly the subject of calls for reform. Some proposed reforms, such as those advocating that jurors be permitted to take notes and to submit questions for witnesses during the trial, are modest designed changes to assist jurors in reaching well-considered judgments, to improve the comfort of the conscripted citizens who serve as jurors, and generally to optimize jury performance and juror satisfaction. Other proposed reforms, such as the reduction or elimination of peremptory challenges and the call for greater use of nonunanimous verdicts, have serious potential costs. The remaining question is whether the increasing scholarly literature on jury behavior will inform popular and political discussion.


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