Plea Bargaining

Plea bargaining is a process in a criminal case whereby the defendant agrees with the prosecutor to plead guilty (or no contest) in exchange for a reduction in charges or a reduction of sentence. By pleading guilty, the defendant gives up the right to go to trial. Contrary to the widespread belief that criminal cases are usually resolved through jury trials, in reality as many as 95% of criminal cases are handled by plea bargaining. This bargaining process has been viewed by some as a rational one in which the participants take into account both the probability of conviction and the likely sentence if the defendant were to be found guilty at trial; the participants arrive at a bargain that is fair to both sides. Critics of plea bargaining have focused on the flaws in the system that distort the process, such as heavy case loads, which cause prosecutors or public defenders to favor plea bargains over trials in almost all circumstances, regardless of the merits of the case. Additional causes for imperfect bargains involve psychological influences that lead to poor decision making. In spite of its importance to the criminal justice system, only a limited amount of research exists on the topic of plea bargaining.

Decision Theory Approach

Decision theory’s concept of value maximization has been used to explain the plea bargaining decisions made by the prosecution and the defense. According to this model, both sides consider both the probability of conviction at trial and the severity of sentence given a jury finding of guilt; multiplying the probability of conviction by the sentence gives one the expected value of going to trial. The desirability of a plea bargain offer is based on its comparison with the expected value of going to trial. For example, consider a case in which, based on the evidence, there was a 50% chance that the jury would find the defendant guilty and, if found guilty, the sentence would be 10 years of imprisonment. The expected value of going to trial would be 5 years (.5 x 10 years). A plea bargain agreement of anything less than 5 years would be a good bargain for the defense, whereas anything over 5 years would be a good bargain for the prosecution. A bargain that would be acceptable to both sides would be close to 5 years. In a perfectly rational world, taking the case to trial and plea bargaining would have the same value, and one might expect the participants to be somewhat indifferent between trial and plea bargain.

Research has shown that plea bargaining participants do, in fact, consider the probability of conviction and the severity of the sentence. Plea bargaining decisions by prosecutors and the defense have been found to be influenced by both variables; however, these two variables alone do not suffice to explain the plea bargaining decisions. Other factors are involved.

Self-Interests of the Bargainers

Certain influences on plea bargaining that are exogenous to the merits of the case affect all the major participants—prosecutor, defense attorney/defendant, and judge. Each of these participants has self-interests outside the merits of the case that might distort the plea bargaining process.


It has been argued, and there is some empirical support for the idea, that prosecutors favor resolving cases by plea bargaining as opposed to trials. Trials involve a much greater commitment of the prosecutor’s time and resources. It has been argued that prosecutors do not have the resources to take any more than a small proportion of their cases to trial; thus, by necessity they must use the more efficient plea bargain to resolve most cases. However, some research has shown that even in districts where the case loads are light, plea bargaining rates remain at the same high level. Even when the case load is low, a prosecutor might prefer not to devote all the time and energy required for a jury trial, particularly given the way prosecutorial performance is evaluated. Prosecutors’ reputations are based on their conviction rates. A case in which a defendant pleads guilty as a result of a plea bargain counts as a conviction for the prosecutor. Thus, for the prosecutor, even if a plea-bargained sentence is under the decision theory expected value, from a self-interest standpoint, it is still desirable because it counts as a conviction.

Public Defenders

Defense attorneys may also have certain self-interests that affect their plea bargaining decisions. One type of defense attorney, the public defender, has much in common with the prosecutor. Like prosecutors, public defenders are paid a fixed salary; whether they plea bargain a case or take it to trial has no financial impact on them. Also similar to the prosecutor, many public defenders have large case loads that would be virtually impossible to handle if any more than a limited few went to trial. Plea bargaining is a means of handling these large numbers of cases. Additional pressure on public defenders to plea bargain comes from prosecutors and judges. Due to the extremely large number of cases that public defenders must handle, there is a great deal of contact with prosecutors and judges. The personal relationships that develop as a result of this contact make them particularly vulnerable to pressure. Refusal to plea bargain on the case at hand when that process is desired by the prosecutor and/or the judge might well jeopardize clients in future cases, who might receive harsher treatment in reprisal.

Privately Hired Attorneys

Privately hired defense attorneys also have self-interests that influence their plea bargaining decisions. Prominent defense attorneys with wealthy clients may favor trials over plea bargaining for financial reasons. Attorneys for wealthy clients are paid by the hour, in most cases. The time spent in preparing for a trial and on the trial itself are all billable hours; in contrast, if a case is resolved through plea bargaining, the billable hours are considerably fewer. Taking a case to trial and winning is important to such attorneys for building their reputation as outstanding trial lawyers; such a reputation is crucial for attracting wealthy clients. Other privately hired attorneys may attempt to maximize their financial gain by emphasizing quantity over quality. Many individuals who are charged with crimes have very limited resources; they lack the means to pay an attorney to do all the background work to prepare a case and present it at trial. However, some defense attorneys take on a large num-ber of these cases at a modest fixed rate and then handle the cases very quickly through plea bargaining. Plea bargaining allows this type of attorney to have a profitable practice based on quantity.


Although most of the actual bargaining goes on between the prosecutor and the defense attorney, the judge plays a significant role. It is the judge who must agree to the terms of the plea bargain; this is particularly true when there has been sentence bargaining as opposed to charge bargaining. As with the other actors in this process, judges may also have self-interest concerns that bias their reactions in the direction of plea bargaining. First, there is the workload issue. Plea bargains are an efficient way to reduce a judge’s workload. A second, more subtle issue concerns a judge’s reputation. A judge’s reputation is harmed when through some judicial error the results of a trial are reversed on appeal. However, when a case is plea bargained, there is no trial and hence no possibility of a judicial trial error. The judge’s interest in plea-bargained solutions often results in direct or indirect pressure on the other actors to plea bargain.


Obviously the defendant has a self-interest in the way the case is handled; it is his or her freedom that is at stake. However, there are a number of issues that affect a defendant’s preference for trial or plea bargain above and beyond the merits of the particular case. There are financial concerns. For those defendants represented by a private attorney, a plea bargain may be seen as a financially less expensive option than the much more costly trial. Furthermore, there may be incarceration time issues above and beyond the potential outcome of a trial. For the defendant who cannot make bail for a relatively minor offense, it is possible that even being found not guilty at trial would result in more jail time than a plea bargain of guilt.

A major concern of critics of plea bargaining is that innocent defendants will plead guilty to a crime that they did not commit. Rather than basing decisions on a rational assessment of the strength of the case and the probability of conviction, defendants base their decisions on faulty information and advice from the actors who are a part of the system. Although it would be extremely difficult to document how frequently innocent individuals actually accept a plea bargain, some experimental research has found that innocent defendants are less likely to agree to a plea bargain than are guilty defendants.

Psychological Influences

In addition to the various ways in which the self-interest of the various actors might distort plea bargaining decisions, a number of psychological influences have been found to distort decision making in any number of situations. For example, how decision alternatives are framed has been found to have a major impact on people’s willingness to take risks. It has often been shown that when the decision alternatives are framed in terms of losses, the deci-sion makers become more averse to risk; in contrast, when the alternatives are framed in terms of gains, individuals are more willing to take chances. Consider the case in which a plea bargain of 5 years is being evaluated in light of the probability of conviction at trial of 50%, with a sentence of 10 years. Defendant A is told that if he goes to trial, there is a 50% chance that he will lose an additional 5 years of his life above the plea bargain. In contrast, defendant B is told that if he were to go to trial, there is a 50% chance that he would gain an additional 5 years of his life as compared with the plea bargain. Although both defendants are facing the same situation, Defendant A will plea bargain to avoid the loss, and Defendant B will take the risk of going to trial for the potential gain. Framing can influence defense attorneys and prosecutors as well as defendants.

When people attempt to form judgments in ambiguous situations, they will often start from some anchor point and then make adjustments. If a prosecutor makes an unreasonable initial plea bargain offer of 20 years, which is summarily rejected, it still acts as an anchor against which subsequent bargains are evaluated. A subsequent offer of 10 years that would have been rejected had it been the first offer now becomes desirable when compared with the 20-year anchor. As with framing, anchoring effects influence prosecutors and defense attorneys as well as defendants.

Various types of attributional biases also play a part in plea bargaining. For example, one type of attribution bias that protects us from feelings of vulnerability is unrealistic optimism. Individuals tend to believe that bad things happen to other people but not to them. It would be quite natural for the defendant to believe that if the case were to go to trial, there would be a verdict of not guilty; this bias would be one of the factors causing a defendant to prefer a trial to a plea bargain.

Limitations of Research on Plea Bargaining

It should be noted that our knowledge about plea bargaining is based on an extremely small body of research. In contrast to other topics in psychology and law, such as juror decision making or eyewitness testimony, for which there are literally hundreds of studies, only a handful of studies exist on plea bargaining. It is particularly surprising that the topic of juror decision making has been so heavily researched, since only 5% to 10% of cases are resolved by jury. In addition to the limited number of studies on plea bargaining, much of the research that has been conducted has been poorly controlled. Much of our understanding of plea bargaining is based on interviews or observations of individuals who were available to the researcher as opposed to individuals selected through systematic sampling techniques. Most of the support for psychological influences is based on generalizations from other bargaining situations rather than on plea bargaining situations themselves. Given the centrality of plea bargaining to the criminal justice system, it is imperative that we increase both the quality and the quantity of research on how this process works.


  1. Alschuler, A. W. (1975). The defense attorney’s role in plea bargaining. Yale Law Journal, 84, 1179-1314.
  2. Bibas, S. (2004). Plea bargaining outside the shadow of trial. Harvard Law Review, 117, 2463-2547.
  3. Fisher, G. (2003). Plea bargaining’s triumph: A history of plea bargaining in America. Stanford, CA: Stanford University Press.
  4. Heumann, M. (1979). Plea bargaining: The experience of prosecutors, judges, and defense attorneys. Chicago: University of Chicago Press.

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