EXPERIMENTAL LAW AND ECONOMICS* COLIN CAMERER ERIC TALLEY Rea A. & Lela G. Axline Professor of Business Economics, California Institute of Technology Professor of Law, USC Law School; Senior Economist, RAND Corporation Institute for Civil Justice PRELIMINARY DRAFT (Do not quote, cite or circulate without permission) December 28 2004 First Version: February 2004 * Forthcoming, Handbook of Law and Economics (A.M. Polinsky & Steve Shavell, eds. 2004). Many thanks to participants at a conference at Harvard Law School for helpful comments and discussions. All errors are ours CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) I. INTRODUCTION Few methodological approaches to the study of law that have received more recent attention than experimental methods. While virtually absent from the pages of law reviews and law and economics journals just a decade ago, experimental studies (or articles purporting to be inspired by the results of such studies) have become a veritable staple consumption good for today’s legal scholars. In many respects, the emergence of experimental methods to analyze law should not be terribly surprising, particularly within law and economics (and affiliated fields). Indeed, over an even longer period of time, experimental methods have become relatively well established in both economics and political science proper – disciplines that served as central foci in generating insights that inform the law and economics literature. In addition, the emerging field of “behavioral economics” has begun to synthesize findings from economics, political science and psychology into a more unified theory of individual and multi-person decision theory. (See, e.g., Camerer et al. 2004). Because psychologists have long depended primarily on experimental methods, these interdisciplinary approaches were a natural fit for such methodological emphases. Indeed, during the last five years, a sub-discipline of “behavioral law and economics” (or BLE1) has emerged that largely echoes the approach in behavioral economics. This very sub-field has similarly enjoyed significant popularity in legal scholarship of late.2 Experimental methods are but one methodological approach within the field of law and economics, and by far the most recent to take root. Most of the initial insights within 1 See, e.g., Jolls, Sunstein & Thaler (1998) for a review. 2 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) the law and economics during the 1960s and 1970s came from applications of core insights from microeconomic theory. Game theorists similarly claimed a piece of the action during the 1980s and 1990s, incorporating insights from repeat play, asymmetric information, and evolutionary selection models into the analysis of law. During this period, empirical methods also began to emerge, particularly as methods for collecting and analyzing data from the court system became more reliable and feasible. In many ways, empirical methods have proven a helpful means for testing the numerous predictions made within theoretical law and economics. Nevertheless, as we elaborate below, empirical approaches suffer from the fact that it is often difficult to stage (much less to observe by happenstance) a truly natural experiment in the real world that implies clear causal conclusions. Because laboratory approaches excel in just this respect, at the very least good experimental designs are likely to provide a complementary and confirmatory check on empirical methods. Our joint enterprises in this essay are (a) to articulate more specifically how and where experimental methods fit into the larger tapestry of legal studies from a social science perspective; (b) to describe contributions that have already been made in the field; and (c) to suggest future courses of inquiry that may well prove fruitful. Before proceeding, a few caveats about our inquiry deserve specific mention. Although the foci of our inquiry may prove helpful to a number of different audiences, we intend our contribution to resonate most centrally with two groups in particular. First, for legal scholars who are not experimentalists by training but who are interested in exploring experimental methods, our review may serve as a valuable reference for A recent Westlaw search, for example, turned up a total of 341 law review articles discussing “behavioral law and economics” during the last 6 years. 2 3 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) generating research questions and guiding experimental design.3 Second, for academics of all stripes who wish to evaluate a piece of experimental law and economics (e.g., referees, reviewers, and so forth), our essay may help provide a framework for evaluating new scholarship for its creativity, novelty, and relative contribution. We would be, of course, pleased if this paper were read by an even broader audience, but such gratification would be strictly fortuitous. A second caveat to our analysis concerns how we make distinctions on subject matter and scope. Because experimental law and economics has a relatively short pedigree (only 20 years or so by even the most generous genealogical counts), it has necessarily drawn from and built upon a vast body of research that used experimental approaches to law, but did not centrally concern economic inquiries per se. Fields such as law and psychology, criminology, and legal sociology have, at intermittent times, employed experimental methods to gain purchase on causal claims about human legal behavior. These literatures, in contrast, have relatively long pedigrees, and we cannot possibly do justice to all of them within the confines of the current essay. We have chosen, therefore, to do justice to none of them, except insofar as they have informed the general approach applied by researchers in experimental law and economics. It is important for us to emphasize that our omission should not be seen to reflect any assessment about the contributions these fields have made to experimental studies, but instead is an artifact of more pedestrian scrivenerial logistics.4 3 Our contribution should not be relied on exclusively, however. Indeed, those new to experimental methods might well benefit from the insights of an experienced co-author, and from other overviews of the experimental approach (such as Croson 2002). 4 Those readers looking for a more general treatment would do well to consult the Volume 4 of the University of Illinois Law Review (2002), which is dedicated entirely to experimental methods in law writ large. 4 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) Our analysis proceeds as follows. Section II discusses general methodological issues surrounding experimental methods in law, including the purpose of experiments, the ingredients of a good experiment, and the central role that experimental evidence is increasingly playing in testing the underlying foundational precepts of economic behavior as it applies to law. Section III then considers a number of specific legal settings in which experimental approaches have proven particularly valuable, such as the study of bargaining in the shadow of the law, the analysis of suit and settlement, and the investigation of jury and judge behavior. In each of these contextual applications, experimentalists have informed the state of academic inquiry substantially, and in many cases experimental approaches have played a central role in spawning affiliated theoretical or empirical literatures. Finally, section IV concludes by offering a series of observations about where experimental approaches might still fruitfully expanded or applied in novel ways to the study of law. II. METHODOLOGY & MOTIVATION FOR EXPERIMENTAL LAW AND ECONOMICS An experiment is the creation of a situation controlled by the experimenter (to some degree), for the purpose of testing a general theory or establishing causality (see Croson, 2002, for a “how to” manual aimed at lawyers).5 As noted above, experimentation, field observation, and theory are ideally complements of one another: done well, each enhances the marginal productivity of the other enterprise. Moreover, 5 Smith (1982) is a seminal discussion of principles of economic experimentation. A useful recipe book is Friedman and Sunder (1993). Bergstrom and Miller (1999) show how to teach an economic principles course using simple experiments. Cumulated regularities are summarized in Davis and Holt (1993) and Kagel and Roth (1995). 5 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) the conditions of the experiment match the assumptions o`f a theory being tested. (Psychologists often refer to this match as “internal validity”). A central feature of any sound experimental design is control. The crucial features of control are (a) the ability to assign subjects randomly to treatments, (b) the ability to operationalize features of theory which are often difficult to observe or control econometrically in field data (and also to create situations of theoretical interest which do not occur naturally or reliability), and (c) the ability to replicate results (which disciplines experimenters, permits accumulation of regularity, and facilitates tests of robustness to design changes). Random assignment is perhaps the most foundational element of a valuable experiment. Explicitly, it is important to be sure that subjects are truly assigned in a random fashion. For example, suppose that subjects are told to sit wherever they like as they arrive, and those in the front row of a lab will act as buyers and those in the back row as sellers. Even though assignment is nominally random, if the early-arriving subjects sit in the front row then buyers will be those who are more punctual and latecomers will self-assign themselves as sellers. If, as seems plausible, early arrivers are likely to have different proclivities than late arrivers, the assignment protocol would not be truly random. It would be easy to draw the wrong conclusion about the effects of buyer versus seller behavior, when the effect is really due to early arrival (an experimental “confound”— a multicollinearity that is easily avoided by random assignment). From the perspective of replicability, experimental economists are frequently preoccupied with following a written script and recording any ad lib instructions that are 6 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) given (often in an experimental log) to permit exact replicability. Such procedures are perhaps a prudent way to address a related problem that has not been explored thoroughly: the underlying “blindness” of an experiment to the hypotheses being tested (which is why being able to replicate the experimental instruction exactly is important). There are subtle ways in which an experimenter’s bias toward or against a theory being tested could influence the results, as well as other subject-experimenter interactions (e.g., male subjects may behave differently in the presence of a female experimenter). Careful analysis of experimental data follows most of the rules of good statistical control of any type of data: Have large samples, make replications as independent as possible, and conduct multiple parametric and nonparametric tests. A complication with many economics experiments is that responses are not independent because subjects interact. If subjects are bargaining in pairs, for example, then data can be analyzed both at the individual level and the pair-wise (dyadic) level. Usually experimental economists are careful about making conservative assumptions about independence. For example, in some cases each experimental session is treated as a separate data point, and tests are conducted with each session-wide summary statistic as a single datum. An early tradition, which is unfortunately waning, is to invite subjects back for a second repetition of the same experiment to see whether experienced subjects behave differently than experienced ones. When equilibria are complicated, we often find that experienced subjects will be much closer to equilibrium predictions6 than experienced ones. This does not imply, of course, that the data from inexperienced subjects are uninteresting. Indeed, the ability to Note that “equilibrium predictions” need not coincide with equilibria emanating solely from rational choice models. Indeed, as we elaborate below, many elements of behavioral economics are themselves amenable to equilibrium concepts. 6 7 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) compare the two groups just helps establish the boundaries of where the equilibrium prediction might work poorly and well. A. Purpose of experiments Experiments are useful for different purposes. In experimental economics, experiments often permit sharp testing of theory when predictions depend delicately on assumptions that cannot be clearly measured from field observation. For example, experiments testing game theory have proved especially useful because predictions often depend delicately on what players know about moves of others and how they value consequences (e.g., Camerer, 2003). Hundreds of experiments have shown where equilibrium concepts predict well and predict badly. These data have also provided lots of raw material to motivate new theorizing about how learning, natural limits on strategic thinking, and social preference like reciprocity explain strategic behavior. Sometimes experiments simply document regularity “pre-theoretically’, as an inspiration for theorizing. For example, early experiments established that even small groups of traders (e.g., as few as three buyers and three sellers) rapidly converge to Pareto-optimal competitive allocations in decentralized trading. This result is surprising because formal models of competitive markets had previously assumed infinitely many “price takers,” so that game-theoretic strategizing is disabled. The experimental regularity shows that surprisingly competitive results can be created by very small numbers of traders when exchange is centralized. This regularity then provoked theories of how strategic interaction would work in small-numbers settings (Wilson, 1985; Cason and Friedman, 1993), and how simple adaptive rules could lead to convergence (Easley and 8 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) Ledyard, 1993; Gode and Sunder, 1997), although this is still largely an unsolved problem. Experiments have also proved useful in giving advice to policymakers about how well targeted policy interventions are likely to work (Plott 1987; Roth, 2002). The inspiration here is very much akin to experimentation in the physical sciences, such as testing of airplane wing designs in wind tunnels, or testing ship designs in “tow tanks” with simulated oceanic waves. While these experiments do not guarantee that a wing or ship which perform well in a wind tunnel or tow tank will be the best design in the air or at sea, they can weed out bad designs at a low cost. A famous recent example is experimental input to the design of telecommunication spectrum auctions, which significantly influenced the actual designs (as did auction theory) in the PCS auctions of the late 1990’s, first in the US then later in many other countries. B. Generalizability Of course, it is important to establish a clear basis for generalizing from the results of an experiment to a specific domain of interest. As Posner (1998) notes: The problem of extrapolating to normal human behavior from behavior in unusual experimental settings . . . is obvious. . . One would like to know the theoretical or empirical basis for supposing that the experimental environment is relatively similar to the real world. That would be the first question an experimental scientist would address. Psychologists use the term “external validity” to describe the extent to which the experimental conditions match those of the setting the results are meant to generalize to. We prefer the term “generalizability” as a reminder that the external, naturally occurring world is complex; there is often not a single “external world” that is different than the artificial experimental world. Furthermore, since 9 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) experimental facts are mean to be part of a three-way dialogue with field researchers and theorists, the crucial component of generalizability is whether a theory carefully distinguishes between behavior of students playing for modest stakes, for instance, and high-priced lawyers in a courtroom. If a theory purports to be general, and its assumptions are carefully created in an experimental design (that’s “internal validity”) then the criticism that the experiment was not meant to apply to students, for example, is really an admission that the theory’s domain of application was not completely specified. A corollary implication of this view is that criticism of an experiment’s generalizability is most productive if it is phrased as an hypothesis about how behavior would differ if the design were changed—i.e., the criticism should be in the form of an alternative design and a prediction about how (and why) the design change would matter. In generalizing from experiments in legal settings, the two most common concerns are the subject pool and the stakes (discussed below). Several studies have shown that experienced professionals typically behave in abstract experiments much like college students do (e.g., Ball and Cech, 1996); so the a priori guess from these studies is that students and experienced lawyers would behave similarly in experiments based on pretrial settlement. Of course, more studies comparing the two groups in legal experiments would be useful. C. Psychology and economics experimental conventions It is important to note that experimental conventions in psychology and economics have historically been quite different (see Camerer, 1996; Loewenstein, 1999; 10 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) Hertwig and Ortmann, 2001), though conventions are being mixed in a fusion as experimenters cross traditional boundaries. Experimental economists tend to insist that subjects’ earnings depend on their choices. Most comparisons between no performance incentives, and low and high incentives, show that paying some performance-based incentive does not usually alter summary statistics like mean responses, but sometimes reduces variance in responses, boredom, and “presentation effects” (e.g., subjects are less altruistic and risk-preferring when playing for real money; see Camerer and Hogarth, 1999; Hertwig and Ortmann, 2001). Paying very large sums typically does not alter behavior much, but a growing body of evidence from paying modest sums, by the standards of developed countries, in foreign countries where incomes are lower will provide more data on whether paying very high stakes makes a difference. Experimental economists also regard deception, which is particularly common in social psychology, as a last resort. The taboo against deception is enforced because of a fear that repeated deception undermines experimental credibility, and may also be transparent to savvy subjects. Experimental economists also prefer abstract descriptions of the experimental setting (to avoid non-pecuniary motives which may be activated by calling an action “defect”, say, rather than “choose row B”). Experimental economists are also more fastidious about reporting all their data in a raw form (to permit skeptical readers to draw their own conclusions), and typically make their instructions and data available— typically on a website, nowadays—to permit low-cost replicability (which also signals the experimenter’s faith in the replicability of their results). Psychologists are more inclined to gather a wide range of cognitive measures, like response times, demographic 11 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) data about subjects, psychometric tests, subjects’ self-reports about motives for their behavior, and brain imaging (e.g., Camerer et al., 2005, and the November 2004 issue of the Royal Transactions of the Philosophical Society B, on “law and the brain”). These distinctions between the two approaches have blurred recently, particularly as experimental economists become more interested in the influence of the description of the experimental setting on behavior. Our view is that good experimentation combines the best of both approaches—extreme care in enabling exact replication, paying some incentive for performance (American subjects are typically paid about triple the minimum wage), full disclosure of all the data with website archiving, and measuring demographic and cognitive variables, and self-reported “debriefings” after the experiment, when those data are easy to gather and potentially informative even when they are not the main focus of study. III. APPLICATIONS We now turn to considering specific applications of experimental approaches within salient legal settings. While time and space considerations prevent us from sampling the entire field, we highlight below those applications that (in our estimation) have proven to be particularly valuable for the study of law and economics. Our first set of applications considers the experimental analysis of bargaining and the Coase theorem, and how economic incentives, information, and entitlement structure affect the ability and proclivity for individual actors to reallocate their rights optimally. The second set of applications concerns experimental studies of the litigation and settlement process – an area that has shed considerable light on our understanding of the processes that select 12 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) cases for litigation. Finally, we consider experimental analyses of jury and judge behavior. In each of these contextual applications, experimentalists have unambiguously informed the state of academic inquiry, and in many cases experimental approaches have played a central role in spawning affiliated theoretical or empirical literatures. A. Contracting, Legal Entitlements, and the Coase Theorem It is difficult to imagine a precept of law and economics that is more central than the much-heralded Coase theorem (Coase 1960). The theorem (in at least one version of its various forms) posits that in the absence of significant transaction costs, the underlying manner in which legal rights are allocated is unimportant for efficiency purposes, since self-interested parties will tend to reallocate rights efficiently through bargaining. Coasean logic is, in fact, foundational to all contracting, and it is therefore not surprising that experimental approaches in law and economics have been particularly focused on contracting behavior. Perhaps contributing to the interest in experimental tests of the Coase theorem is the concept’s own fluidity. As a conceptual premise, the Coase theorem is as easy to understand as it is difficult to apply. Indeed, as Coase himself recognized, the most interesting cases are those in which transaction costs are significant, and bargaining in the shadow of the law need not be efficient. Experimental law and economics scholars have devoted considerable attention to numerous manifestations of the Coase theorem, in part to identify what those cases are. Although their contributions are too numerous to catalog here, we can at least provide a sampling. 13 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) Simple Bargaining Environments with Perfect Information: Perhaps the most natural experimental environment in which to test the predictions of the Coase theorem is in a simple two-party bargaining framework. Early pioneering work in the field (e.g., Hoffman & Spitzer 1982; 1985) largely confirms the zero-transaction costs predictions of the Coase theorem in simple experimental settings. The Hoffman/Spitzer experimental design involved a designated “controller” who could unilaterally choose among various social allocations of money, which differed both in their aggregate level of compensation and in their distribution. The experimenters varied the determinants of how one was designated a controller, ranging from simple random designation to an “earned” right through a series of backwards induction games. Finally, the parties were allowed to contract for side-payments prior to the controller’s choice of social allocation. The authors found that while the method for determining the controller significantly affected distributions between the parties, nearly all the dyads were able to contract into the socially optimal outcome. This work (and various follow-on efforts) gives reason to be sanguine about the ability of parties to overcome endowment effects. Private Information One factor that early Coase theorem experiments described above did not attempt to control for was the information structure of the bargaining environment. This omission is potentially significant, since it is well known from the bargaining literature (e.g., Myerson & Satterthwaite 1983) that private information leads to generic inefficiencies. More recent experimental work (e.g., McKelvey & Page 2000) has confronted this challenge more directly, testing the Coase theorem in contexts where 14 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) asymmetric information pervades the bargaining environment. McKelvey & Page, for example, find that property rights can be “sticky” under asymmetric information, in that efficiency-enhancing transfers from low valuers to high valuers frequently fail to be consummated unless the mutual gain is significantly greater than zero. This finding is largely consistent with the predictions of asymmetric information game theory. In a related twist on this approach, Croson & Johnston (2000), studied Coasean bargaining experiments involving asymmetrically informed parties, but the experimenters varied the way that the underlying legal entitlement was protected. For some subjects, a legal entitlement was protected by a property rule (which gives its owner the right to enjoin conflicting use by others). For other subjects, the right was protected a less certain rule (such as a probabilistic entitlement or a liability rule that allows the non-owner to appropriate the right non-consensually in exchange for paying damages). Johnston & Croson find that partial entitlements of this type (particular uncertain ones) to lead to more efficient bargaining outcomes than strong property rights, a prediction that is consistent with rational choice theory predictions with asymmetric information (Ayres & Talley 1995; Johnston 1995). Endowment Effects During the period in which the Coase theorem experiments were ongoing, research motivated through law and psychology was exploring a related phenomenon that has come to be known as the “endowment effect,” a term that embodies experimental findings about how ex ante possession appears to affect valuation decisions. Explicitly, the endowment effect reflects experimental (and empirical) evidence that the maximum 15 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) amount a person would be willing to pay to procure a good is often significantly less than the minimum amount she would be willing to accept to part with the same good, in contrast with most assumptions of the rational actor model that possession does not affect value. It is a phenomenon that has been detected in numerous experimental settings (for a recent meta-analysis, see Horowitz & McConnell 2002). While the endowment effect was originally the province of prospect theorists in economics and psychology (e.g., Kahneman, Knetsch & Thaler 1990), experimental legal scholars soon recognized (and exploited) its relevance as well. Indeed, the existence of significant endowment effects may have important implications for both our positive understanding of legal rules and how such rules should be designed optimally. Most generally, because the endowment effect retards efficient trade, it is more incumbent on legal orderings to calibrate allocations efficiently from the outset. As such, considerably more thought would have to go into determining how to set default rules in contracting (Korobkin 2002), whether to protect entitlements with strong or weak protections (Rachlinsky & Jourden 1998), and in whom to vest entitlements to begin with. The set of challenges introduced by the endowment effect is made more intriguing by the fact that it appears to be a fairly context-dependent phenomenon. In particular, the effect appears most pronounced in situations where the entitlement at question has few market substitutes (Shogren et al. 1994), when it has significant use as well as exchange value (Kahneman, Knetsch and Thaler, 1990);7 when subjects believe their entitlement was the result of merit rather than luck (Loewenstein & Isaccharoff 1994); and when subjects have had little practice or other familiarization with the experimental design 16 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) (Plott & Zeiler 2004). These contextual caveats are important for legal policy makers, since exporting lessons from the laboratory to the outside world is often a hazardous business. Nevertheless, there appear to be many legal environments where the endowment effect is a plausible and important phenomenon. One area of research that has yet to be significantly developed is the intersection between theories of asymmetric information and endowment effects in legal bargaining contexts. Many of the existing contributions in one field or the other can be justifiably criticized for concentrating too myopically on one account or the other, without attempting to discern between them. This is particularly problematic, since many of the situations in which the endowment effect is most pronounced correspond precisely to where private information is likely to be a factor.8 B. Litigation and settlement Another robust area for experimental research in law and economics has been on the litigation process itself. The process of trials is the unique foundational feature of the law as an institution, and it should therefore not be surprising that it has garnered attention from not only legal scholars but also from other social scientists interested in strategic interaction. As we discuss below, one particular area of study in particular – that of the “self-serving bias,” is intimately related to the law and economics of suit and settlement. 7 Most experimental evidence suggests that the endowment effect is not present when the underlying right is solely or principally a store of value. A few experiments, however, have detected an effect when the underlying value is itself uncertain (e.g., van Dijk & van Knippenberg 1996). 8 For example, as Shogren et al. 1994 demonstrate, the endowment effect is strongest in situations where there are few if any ready market substitutes for a good. Similarly, the strategic importance of private valuation is substantially reduced (and often eliminated) when there are numerous market substitutes for a good in question. 17 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) Perhaps the most long-standing line of research in the trial process was begun by psychologists interested in the effects of optimism and “self-serving bias” in affecting decisions within risky environments. Building on pioneering work in psychology (e.g., Roth & Murnighan 1982), a number of legal, economics, and psychology scholars have explored the degree to which individual litigants appear to skew their expectations about trial in a manner that favors their own case. In perhaps the most familiar set of experiments (Babcock et al, 1995; Babcock, Loewenstein & Issacharoff, 1997; Babcock & Loewenstein 1997), subjects were instructed to act as attorneys, and read a narrative involving a personal injury dispute between two potential litigants, in which damages were known to be $100,000 but liability was in doubt. While a group of control subjects read these materials without knowing whether they would ultimately be asked to defend the plaintiff or defendant, the treatment group was told in advance which side they would ultimately represent. Information was then elicited from both subject sets about (a) what amount of money was likely to be the most “fair” to remunerate the plaintiff; and (b) what amount of money they predicted would be awarded by a real judge (who had read the facts previously and who had issued an independent judgment9). Finally, the parties were afforded an opportunity to settle their case during a bargaining period that preceded the non-consensual imposition of an outcome. In virtually all permutations of this experimental setting, subjects who were informed of their role beforehand exhibited economically and statistically significant differences from the control group. For example, treatment subjects differed from control counterparts both in their assessment of the fair outcome and of the judge’s ultimate 9 Typically, subjects in these studies were awarded monetary prizes for the accuracy of their predictions about judge behavior. 18 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) decision by approximately $18,000, while control subjects actually exhibited no difference (or even a negative difference). More to the point, treatment subjects exhibited a significantly lower settlement rate, and a significantly longer period to settle when they could reach an agreement. More recent experimental efforts to test the robustness of this finding have provided evidence that self-serving biases are also present when the extent of damages (rather than liability) serves as a source of potential disagreement. Babcock & Loewenstein (1997), for example, find that the same qualitative variety of self-serving bias also can be found in attorneys and experienced negotiators (albeit sometimes in a smaller magnitude). In other recent studies, Babcock & Pogarsky (1999; 2002) find that it is possible to manipulate the “gap” between plaintiffs’ and defendants’ assessments of a case by imposing a damages cap that constrains the range of feasible settlements. Additionally, the authors find, quite interestingly, that the imposition of an exceedingly generous cap on damages had the reverse effect, increasing disagreement and discouraging bargaining. This finding suggests a possible interaction between litigant “optimism” on the one hand, and anchoring effects on the other (a cognitive behavior discussed more fully below).10 Finally, at least some preliminary work has been done exploring processes by which procedures may de-bias litigant optimism. For instance, Babcock, Loewenstein & Issacharoff (1997) find that a simple but effective de-biasing instruction is to urge litigants to consider the relatives strengths of the opponent’s case or the real possibility that the judge may rule for the other side. Debiasing (and reduction in costly delay) also occurs when subjects are assigned to their bargaining role after reading the case materials, which implies that the self-serving bias is created by encoding of the case facts 19 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) as they are being digested, rather than by the role assignment per se. Still few experimental results exist, however, mapping out the robustness of de-biasing mechanisms. The literature on self-serving biases in litigation plays a particularly interesting role in providing experimental support for a key theoretical account within law and economics about how cases proceed to litigation. The famous Priest-Klein (1984) hypothesis about litigation posited a theoretical model in which relatively “optimistic” litigants fail to settle their cases, but pessimistic ones litigate. The self-serving bias literature presents credible evidence for a version of the Priest-Klein hypothesis in which all litigants exhibit some optimism, although some exhibit more than others. Interestingly, many of the same predictions from their theoretical mode (such as the well known 50% plaintiff victory prediction at trial) emerge from models of self-serving biases. Interestingly, this may be an area where theoretical work by law and economics scholars helped to motivate later research by non-legal scholars about litigation behavior. A an approach complementary to that reflected in the self-serving bias literature for analyzing suit and settlement comes from the theoretical literature positing that information asymmetries retard settlement (e.g., Reinganum & Wilde 1986; Spier 1994).11 Under this approach, some parties act as tough bargainers not because they are overly optimistic, but rather because they possess proprietary information about the strength of their case. Similar to the endowment effect literature, the experimental results 10 See subsection 3, infra. While information asymmetries are undoubtedly important, note that the debiasing effect of assigning bargaining roles after reading case facts in Babcock et al. (1997) shows clearly that the creation of selfserving bias while encoding information is important too. That is, two parties reading the same case facts with different roles in mind can create a perception asymmetry (like fans on opposite teams watching a sports event both thinking the refereeing is biased against them) which will have similar implications to a true information asymmetry. 11 20 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) in self-serving bias literature may, in part, embody some aspects of private information. For example, subjects pre-informed of their hypothetical roles may selectively search for facts that support their client’s case, glossing over those that are either neutral or support the other side’s case. Entering negotiation, then, each side may have some informational advantages over the other. To date, there appear to be few experimental designs that are capable of disaggregating informational from cognitive impediments to settlement.12 As noted earlier, one important use of experiments is to help design or evaluate how well legal institutions work, in settings where we can control for endogeneous adoption and evaluate efficiency directly. Babcock and Landeo (2004) did bargaining experiments to examine the effects of pre-settlement escrows (as studied by Gertner and Miller, 1995). In their experiments a plaintiff learns of a damage amount drawn from a commonly-known distribution; in the interesting case the defendant knows only the distribution. Both plaintiff and defendant make secret settlement offers. If the offers overlap they settle immediately; otherwise two rounds of bargaining proceed, incurring fixed costs. If no settlement is reached they “go to trial” and the plaintiff is awarded the actual damage. They found that the escrow mechanism increases settlement from 49% to 69% and lowers pre-trial legal costs by about half. Furthermore, the results are roughly consistent with many numerical predictions of the Gertner-Miller model. C. Adjudication, Jury Behavior and Judge Behavior Another fertile area of research for experimental law and economics scholars has been in the behavior of juries and judges. We consider them each, one at a time. Unlike 12 A few experimental studies find results consistent with the informational account of settlement failure in analyzing the English versus American rules on fee shifting. See Coughlan and Plott (1997). 21 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) each of the foregoing areas, however, the study of judges and juries has a significantly more disorderly nature to it. While there are a number of interesting individual findings in this area, they are more difficult to weave into a larger, unified descriptive tapestry. We therefore content ourselves merely with describing the various contributions that exist here. Jury Behavior, Voting, and Social Pressure Game theorists have long been interested in jury decision-making, and in many instances theoretical contributions in the field have inspired subsequent efforts by experimentalists to test the theory in the laboratory. In one notable example of this trend, a relatively recent literature (emanating largely from economists and political scientists) has called into question the relative wisdom of unanimous vote requirements the jury setting. In a well-known article, Fedderson & Pesendorfer argue that strategic voting by juries may lead to more convictions under a unanimity rule than under a majority rule, since individual jurors under a unanimity rule may feel particularly hesitant to be the pivotal hold-out in a vote (Fedderson & Pesendorfer 1998). Others (such as Coughlan 2000) have challenged this assertion, noting that most juries engage in deliberation, and through such pre-vote deliberation juries are significantly more likely to transmit important information to others, thereby decreasing the chances of such perverse predictions. A recent experimental study by Guarnaschelli, McKelvey & Palfrey (2000) attempts to test that claim in an experimental setting of hypothetical jurors. They find, consistent with the Fedderson & Pesendorfer thesis, that juries are more likely to vote strategically under a unanimity rule; however, the aggregate effect of this strategic 22 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) behavior does not appear consistent with the Nash prediction of higher conviction rates under a unanimity rule. The tendency of juries to vote strategically has interesting parallels to the early pioneering work in psychology on social pressures to conform. Solomon Asch’s wellknown experiment in which confederates are successfully able to tip majority opinion, while not directly about law, has been cited by many as an example of the non-Bayesian biases that juries often face (see Asch 1956; Kuran & Sunstein 1999). To date, however, there have been few efforts by experimentalists in law and economics to incorporate this phenomenon into a broader analysis of strategic voting. Hindsight Biases Another important cognitive heuristic that has been shown to be important in legal settings is hindsight bias: the tendency for individual decision-makers to be overconfident about the ex ante predictability of a particular event, knowing that such an event did in fact come to pass. In more pedestrian parlance, the hindsight bias is roughly akin to the practice of “Monday morning quarterbacking” – proclaiming foreknowledge of a solution to a difficult problem that has since become obvious in hindsight. Motivated by early experimental results in psychology (e.g., Fischhoff 1975), a number of legally oriented scholars developed experimental settings to determine whether jurors are also subject to hindsight biases (e.g., LaBine & Labine 1996; Kamin & Rachlinsky 1995). These experiments (which sometimes involved financial incentives) asked jurors to assess whether a particular act of nonfeasance constituted negligence. Those in the control condition were given information about the relative costs and benefits of action, 23 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) while those in the treatment condition were given the identical set of facts ex post, along with information that harm had actually occurred subsequent to the defendant’s nonfeasance. In each study, subjects in the treatment group were consistently much more willing to find the existence of negligence than those in the control group. Prescriptively, the finding of a significant hindsight bias among jurors may provide some basis for a number of concrete institutional responses, such as altering the legal nature of negligence, obviousness or any number of legal standards that turn on retrospective assessment of ex ante likelihood. But moreover, the finding begs the question of whether there might be ways to minimize or eliminate the bias with procedural changes in court. In this respect, some experimental findings (e.g., Viscusi 1999, 2001) indicate that judges are substantially less susceptible to hindsight biases than are jurors, suggesting that encouraging bench trials may be an opportune way to reduce the hindsight bias from legal proceedings. This conclusion, however, is not free from debate, and other studies (e.g. Guthrie, Rachlinski, Wistrich 2001 ) find that judges are also susceptible to hindsight biases (albeit perhaps in a lesser degree than jurors). Additionally, there may be simple forms of jury instructions that have the effect of diffusing (or at least dampening) the bias. For example, one study finds that a warning to jurors avoid second guessing the defendant’s actions or being “Monday-morning quarterbacks” substantially reduced the prevalence and degree of hindsight bias in subject jurors (Stallard & Worthington 1998). 24 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) Anchoring Finally, as noted above, at least some of the experimental literature on attorneys has touched on a phenomenon known as the “Anchoring Effect,” a behavioral regularity that is more routinely highlighted in jury experiments. Anchoring refers to the process by which an individual decision maker gravitates to a reference point that she subsequently uses as an initial condition for arriving at a final decision. The effects of anchoring appear to be especially strong in the context of damage awards given by juries. These decisions are typically made complex by the lack of familiarity that juries have with the range of damages that are appropriate within a given class of cases. The lack of an “upper support” on the set of damages can invite manipulations by interested parties to distort jury decision-making. For example, it is now well documented in a number of experimental studies that both statutory damage caps as well as specific monetary requests made by plaintiff attorneys can provide an anchor from which jurors may work, in awarding both compensatory damages and (in particular) punitive damages. (Hastie, Schkade & Payne, 1999; Robbennolt & Studebaker 1999). And, while anchoring appears to be predominantly a danger for juries and courts, litigants themselves may also be susceptible to the effect (Babcock & Pogarsky 1999). As with the hindsight bias, anchoring effects appear to be more pronounced with lay juries than with professional judges. IV. LOOKING AHEAD Although the universe of experimental studies of law is now becoming sizeable and is still growing, there remains a considerable stock of “low hanging fruit” for legally 25 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) oriented experimentalists to harvest. Although we have neither the time nor space in this essay to offer an exhaustive inventory,13 future research possibilities include both methodological and substantive dimensions, which we briefly explore below. Methodologically, as noted above, very few experimental studies of law have attempted to discern how subjects behave when repeating experiments. Not only would such information convey significant information about how learning and experience affect performance, but it would also contribute to the power of experimental findings, by allowing researchers to infer “within subject” treatment effects and subject-based fixed effects that are not easily observable with strict cross-sectional analysis. Another promising methodological approach is to use internet-based experimental instruments to measure individual responses to experimental protocols. While this form of data collection has obvious drawbacks (such as a reduction in control and perhaps more selection bias in responders), it allows experimenters to access a much broader crosssection of subjects than is frequently available in university settings. (See, e.g., McCaffrey & Baron 2004). In a similar vein, a rapidly emerging development in experimental economics is the use of field experimentation, in which some elements of control are imposed on a naturally occurring situation. In one study of this sort, Camerer (1998) placed large ($500-1000) bets at a horse racing track (and cancelled them at the last minute) to determine whether such activity would cause cascade effects in other bettors (e.g., Bikhchandani et al. 1992). Control came from the fact that which of two matched-pair 13 Nor, to be brutally honest, do we have the inclination to give away our own best research ideas for the dubious sake of spicing up a concluding section whose text (and footnotes) no one -- except for possibly the editors of this book -- is otherwise really going to read anyway. 26 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) horses were bet on was randomized by a coin flip.14 Another cross-cultural study did experiments on simple bargaining games in 15 small-scale societies to investigate the link between cultural practices and fairness norms (Henrich et al., 2004). Field experimentation is not completely foreign to legal scholarship. For example Ayres (1991) explored the prevalence of racial profiling in new car markets by sending a racially diverse set of confederates into automobile dealerships to bargain for new cars using identical bargaining strategies. Using visits to identical dealerships to establish control, he finds that racial minorities tended to pay both higher first offers and higher final prices than white males. Bertrand and Mullainathan (2004) did a similar “audit” study, sending resumes to employers which were identical except for different black and white applicant names, to investigate discrimination in hiring. The principal attractions of field experiments are that they extend the reach of the experimental method to the subject pools we are often most interested in. However, field experiments are often criticized for failing to procure adequate informed consent from the target populations.15 Substantively, legal scholars are in a particularly opportune position to make contributions about how law should respond to behavioral patterns that are frequently observed in experimental settings. Indeed, if nothing else, the legal milieu is one of the most elaborate and pervasive of contexts in which many (or even most) people interact. As noted above, we are still far from determining the contextual boundaries of a number of experimental findings (such as the endowment effect), and underlying questions about Similarly, Lucking-Reilly (1999) created internet auctions for “Magic” playing cards with different auction structures to test predictions about the influence of reserve prices and other variables on bids. Control came from the fact that subjects who entered the different auctions presumably did not self-select which one to enter. 14 27 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) the generalizability of experimental findings still substantially hinders informed legal reform. More work by legal scholars can help to investigate the precise legal contexts such effects are largest, how they interact with the substantive underpinnings of legal rules and standards, and how legal rules may be best designed to avoid situations where individual decision making is likely to be untrustworthy. Another area in which legal scholars are in a prime position to contribute to experimental law and economics is in the enterprise of discerning how (and whether) legal structure itself can help not to avoid triggering cognitive inconsistencies, but rather can help to de-bias individual decision-making (Jolls & Sunstein 2004). As noted above, for example, some studies have found that relatively simple manipulations can dampen – and in some instances eliminate – cognitive biases, such as jury instructions (e.g., Simon et al., 2001)16 or the introduction of a fiduciary-like agency relationship (e.g., Arlen et al. 2002). Despite these isolated findings, there is surprising little experimental work to date exploring on how legal institutions might play a role in accomplishing this task. Finally, a topic that has enjoyed relatively robust attention among legal scholars in recent years – that of extra-legal “norms” of behavior – has proven to be ripe stalking grounds for experimentalists as well. A number of recent studies by economists (Fehr, Fischbacher & Gächter, 2002; Bohnet, Frey and Hück, 2001) have suggested that norms of cooperative behavior and legal / contractual sanctions may have interesting interaction effects. The interplay between behavioral norms and law’s dual expressive and sanctioning qualities has been taken up by legal academics as well of late in experimental 15 Harrison and List (2004) and Bertrand and Mullainathan (2004) provide more examples and a taxonomy of features of field experiments. 16 Simon et all, 2001 find that simple “consider the other side” jury instructions can help to mitigate the effects and incidence of constraint-satisfaction reasoning (somewhat akin to cognitive dissonance). 28 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) settings (Bohnet & Cooter 2004, McAdams & Nadler 2004). Nevertheless, there is still remarkably little known about the extent to which legal regulations and extra-legal norms complement one another, substitute for one another, or neither. 29 CAMERER & TALLEY, EXPERIMENTAL LAW AND ECONOMICS (DRAFT: Do not quote, cite or circulate without permission) REFERENCES 1. 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