گروه تصمیم گیری: تجزیه و تحلیل اقتصادی از نفوذ اجتماعی و تفاوت های فردی در داوران تجربی

In jury decision-making, individual viewpoints must converge to reach a group consensus. Convergence of viewpoints may reflect reasonable compromises, for example if jury deliberations reflect informational influences and social learning which allow individual jurors to correct biases, misunderstandings and/or imperfect recall of evidence. Conversely, some individuals may converge towards others’ viewpoints because of normative influences including peer pressure and preferences for conformity and these can generate biases in the final jury judgements. This paper presents experimental data showing that groups do have a significant tendency to compromise in jury-like settings. Econometric evidence shows that group characteristics, including the presence of acquaintances and strangers within the jury group, affect the extent of compromise. The implications are that jury deliberations may be biased by factors not relevant to a specific case, limiting the objectivity of jury decisions.

The integrity of the justice system is a vital component of a country's institutional structure: many economic transactions are facilitated by the existence of the legal and justice system, which acts as an external enforcer for contractual agreements. The jury decision-making process also has many similarities to group decision-making in economic settings, for example decisions by policy-making committees or groups of investment managers, and so insights into juries may be applicable to the study of decision-making in other groups. The justice system aims to treat all individuals fairly and equally, and therefore the hope is that a jury would reach the same verdict on a particular case, regardless of its composition. If two different juries can come to substantially different verdicts simply due to differences in their membership then the justice system is undermined, with repercussions for society and the economy. Although the presence of such inconsistencies would be extremely damaging, the identification of the causal factors behind this problem would help policymakers to make remedial changes to the justice system. There are debates about the pros and cons of using juries to decide outcomes and the jury system does have significant limitations. Jurors may be susceptible to bias especially if a defendant has received a lot of negative publicity – and though voir dire (pre-trial questioning of jurors) is meant to reduce the likelihood of selecting a biased juror, the voir dire process is not always effective ( Cahoy and Ding, 2005). Goyal (2007) shows that the process of deliberation can introduce bias into the final decision when suggestible individuals’ opinions are unduly swayed by the views of the others. There is also the problem of lack of effort or ineptitude from jurors, especially if incentives are not strong. In Visher's (1987) interviews of 331 jurors many jurors were swayed by irrelevant/extra-legal issues e.g. attitudes, victims’ and/or defendants’ characteristics, and evidential issues e.g. cases involving the use of force. These influences may limit the competence and objectivity of jurors. Also most jurors decide in direction of initial majority. This may be because social influences are important. In some cases litigants view jury behaviour as random, suggesting that there may be significant doubts about the objectivity of jury decisions ( Cahoy and Ding, 2005). The use of a jury rather than a single judge can be justified on the basis of the Condorcet theorem: given imperfect information, as the size of a decision-making group increases, it is more likely that the group majority will reflect a correct judgement of probability of a given event, though only if the individual votes are uncorrelated (Ladha, 1995, Surowiecki, 2005 and Austen-Smith and Banks, 1996). In this way, the aggregation of private information and judgement leads to more effective decision-making. Groups of randomly selected, heterogenous people will bring a greater variety of personalities, perspectives and past experiences to a case, reducing a priori bias. A jury's ex post bias may also be smaller than a single judge's because the process of deliberation increases the likelihood that all the evidence and arguments for a case are remembered and considered before a decision is reached ( Pritchard and Keenan, 2002). Juries may be a buffer against elitism and political influence and jurors may be better able to judge their peers than legal professionals ( Cahoy and Ding, 2005). Group decisions are also more effective when random outliers are diluted, implying a larger group is better than a small one – though this may be undermined by strategic voting, in which case individuals may not be revealing their private information ( Feddersen and Pesendorfer, 1998). Limitations on the efficacy of group decision-making occur when votes are not statistically independent, and this can be characteristic of real-world juries – e.g. the effectiveness of majority rule decreases as the correlation between voters increases (Ladha, 1995 and Dawkins, 2003). One potential constraint on jury deliberation is the impact of opinions of sub-sets of jurors. A minority of individuals can unduly influence a jury's decision. If we can understand how and why they might do so, it may be possible to suggest changes to the justice system to improve jury objectivity. Also, if a jury is unduly swayed by the opinions of an individual or small group then the process of deliberation will be ineffectual. In their post-trial study of 225 criminal jury deliberations, Kalven and Zeisel (1966) found the first ballot decided the outcome, suggesting that the process of deliberation had limited impact. The efficacy of juries may be better in some situations than others. Jury size for example may have a significant influence. Mukhopadhaya (2003) observes that 12 person juries may be better than 6 because there will be more information/perspectives from larger juries. Conversely there may be a free-rider problem if individual jurors rely on the efforts of others and don’t make an effort themselves. Grofman and Feld (1976) observe that a smaller jury may lead to substantial cost savings in terms of jury days and trial processing time but they identify the importance of clique avoidance, especially when jury panels serve on a number of cases leading to possible overlapping of jurors across multiple cases. In experimental work for this paper, participants were collected into small mock juries of five or six individuals. They were asked to read the evidence for a case and reach – firstly an individual verdict, and secondly – after deliberation, a unanimous group verdict. The purpose of the experiment was to investigate whether different juries examining the same case would come up with the same verdict and, if not, to identify some of the factors which caused them to diverge. In particular, the analysis examines the impact of social influences on jury deliberations and also extends the experimental approach into the analysis of evidence from a civil case (MacCoun, 2005).

Overall the experimental evidence presented here suggests that a combination of individual and group characteristics affected the convergence to consensus for the mock juries studied. The strongest compromises were observed firstly, in jurors with higher degrees of venturesomeness and receptiveness to new ideas; and secondly, in groups comprising of more strangers and acquaintances than friends. Previous studies have focussed on the impact of individual heterogeneities. Although these may be uninformative and irrelevant to the task in hand, they can have a significant effect on an individual's tendency to conform. This is perturbing for the integrity of jury decision-making, because it suggests that verdicts may be dependent on the jury chosen for the trial, rather than solely on the evidence presented. In this analysis, some individual characteristics which might have a positive impact have been identified, specifically venturesomeness and receptiveness to new ideas. These may be positive traits within the context of jury deliberations if they are associated with a form of informational influence when jurors’ compromises reflect a willingness to consider alternative viewpoints and correct individual biases and mistakes. On the other hand, the evidence shown here about increased willingness to compromise in the presence of acquaintances and strangers may reflect an impact of less constructive normative influences and conformity preferences; these will predominate if jurors attempt to gain approval from others by adjusting their judgements to a majority view. A significant problem with this analysis is that the estimations do not control for the factors which influence an individual's initial verdict: if an individual chooses an extreme initial verdict then they will be an outlier in their group and so forced to compromise more, so factors which cause extreme initial verdicts will confound the results regarding compromise. It seems unlikely that the number of strangers in one's group would affect one's initial verdict, particularly because individuals were not allocated to groups until after they’d chosen their individual verdict. However this endogeneity problem is significant for the personality trait variables, which are much more likely to affect initial verdicts. For example empathetic individuals may be more likely to choose a generous initial verdict, so are more likely to be an outlier in their group and so are under more pressure to conform. More research into the effects of personality traits on individual verdicts is needed to address this problem, or alternatively a way of controlling for the extremity of one's initial verdict needs to be found. Further research is needed to investigate the extent to which the findings are applicable in real-life juries. Even if there are inconsistencies between different juries’ verdicts the use of juries may still be justified for other reasons, for example Cooter and Ulen (2004) argue that juries reduce the opportunity for corruption, as a larger group of decision-makers means that bribes and threats are less concentrated. These results may also have implications for group decision-making made in an economic setting, suggesting that network relationships and personality traits may prevent an individual remaining objective about a particular question. Future research could develop social influence and opinion convergence models to extend the analysis of the interactions of compromise versus conformity in group decision-making. Notable differences between this experimental set-up and real juries include the time limitation imposed on deliberation, the smaller amount of evidence used and the small size of the juries used, all of which were adopted for practical purposes. Time limits may have prevented the mock juries from fully examining the evidence, but in reality the mock juries analysed here came to their conclusion before the end of the time period. This suggests that the time constraint did not pose any significant problems and so should not have adversely affected the reliability of the results. The small amount of evidence used would have, if anything, helped the jurors to accurately remember all the evidence; any difficulties in absorbing and recalling this information would only be amplified with more evidence, so it seems likely that results would be robust with more evidence. Although Klevorick and Rothschild (1979) show that the use of smaller juries does not substantially affect the final verdict reached, their model does not take into account any difference in deliberation between small and larger groups. Deliberation may be less effective with fewer individuals because the jury will have a smaller pool of extra information and opinions to work with, and also because each individual represents a greater proportion of the group and so certain individuals may be able to exert more influence. More work needs to be done using 12-person juries in order to find out whether the results found here apply with larger juries. The findings from this study have broader economic significance beyond the realm of jury decision-making. In essence, social influences can be positive if they encourage compromise but are negative if they generate conformity. In many contexts, decisions are made as the outcome of group deliberations – in contexts ranging from company boardrooms to government policy-making teams to community decision-making committees. It is important to establish whether compromise in these contexts is an outcome of individuals’ insights about their own biases and mistakes and/or reflects the impact of subjective normative influences that encourage people to seek social approval by conforming to majority views.