Digging into the foundations of evidence law.

• Author: Kaye, David H.
• Position: Book review

THE PSYCHOLOGICAL FOUNDATIONS OF EVIDENCE LAW. By Michael J. Saks and Barbara A. Spellman. New York and London: New York University Press. 2016. Pp. xiv, 241. Cloth, $89; paper, $38.

INTRODUCTION

Professors Michael Saks (1) and Barbara Spellman (2) have produced a gem of a book. A concise, cogent, and thoughtful introduction to the major rules of evidence, The Psychological Foundations of Evidence Law glitters in the light of ideas from social and cognitive psychology. PFEL, as I will abbreviate it, is an eminently accessible (3) book that evidence professors should assign to their students; that psychologists seeking research questions about evidence law should consult; (4) that litigators seeking to sharpen their persuasive powers should peruse; and that judges engaged in screening improperly prejudicial evidence from jurors should examine. In Saks and Spellman's words, the book

explores a number of important practices from evidence law about which psychology does, or could, have a lot to say to illuminate the underlying assumptions, and evaluates whether those assumptions are consistent with the psychological research or whether the law's goals for evidence doctrine could be achieved more successfully with a modified rule or a different rule or no rule at all. (p. 3) This Review has three goals. Part I surveys PFEL's scope and provides examples of several of its conclusions. Part II focuses on one psychological (or logical) model that the book presents for understanding two fundamental concepts in evidence: relevance and probative value. It digs into the foundations of these concepts more deeply to expose a slightly different conception of the probative value, or, more metaphorically, the weight of evidence.

1. EXPOSING THE FOUNDATIONS

   At a granular level, the sheer number of rules of evidence is vast, (5) but PFEL surveys the major federal rules with emphasis on probative value, counterweights to relevant evidence, character evidence, competency of witnesses, privileges, impeachment, hearsay, limited admissibility, (6) and expert and scientific evidence. (7) Throughout these areas, PFEL maintains that psychology can improve on rulemakers' "assumptions, impressions, anecdotes, and reasoning about human behavior" in two ways (p. 16)--by conducting controlled experiments (simulations with mock jurors and "similar studies to take place in the setting of actual trials") (8) and by "borrow[ing] from the findings of more basic empirical research, or from theoretical knowledge about human perception, memory, and information processing" (p. 17). In particular, PFEL brings to bear findings about mental contamination ("how prior knowledge can bias future judgments in an unwanted manner"), (9) dual systems reasoning (System l's fast and frugal heuristics (10) versus System 2's "slower, conscious, and reflective" processing) (p. 20), information integration theory ("how people combine bits of information into a final judgment") (p. 43), motivated reasoning (p. 208), contextual bias (p. 26), attribution theory (p. 79), "weapons of influence" (pp. 40-41), and "diffusion of responsibility" (p. 216). It also includes specific studies on such topics as the impact of gruesome pictures (pp. 64-65), observer or expectancy effects in forensic science, (11) lie detection (pp. 122-28), decision aids for expert evidence (pp. 226-27), and framing effects in the presentation of statistical evidence (pp. 221-22).

   On the basis of such theory and findings, Saks and Spellman give the modern trial process high marks in some respects. As they see it, "[t]he rules came into being to rein in the inevitable excesses of lawyers in an adversarial system" (p. 11). That is, Saks and Spellman embrace the theory of several legal historians that "limits had to be placed on what ... lawyers would be permitted to do" (p. 11) in an adversarial system as opposed to an inquisitorial one, in which these one-sided lawyers played a more ancillary role. But they believe that the adversarial system alone is not the full explanation. The presence of impressionable jurors also matters. "[P]ut the adversary process together with juries, and evidence rules become a necessary device for restraining lawyers, thereby protecting jurors from being deceived or misled" (p. 11). They then find that, as a whole, the rules of evidence perform this restraining function very well:

   [T]he rules that govern the trial have the effect of blocking or dampening the use of influence techniques that do not contribute to the (relatively) rational resolution of the disputed issues. In their effort to make trials more information-based and more rational, the rulemakers have done quite well by limiting the possibilities for using the most powerful tools of persuasion and influence, (p. 41) Those tools, in the nomenclature of social psychologist Robert Cialdini, are the "six weapons"--reciprocation, (12) commitment and consistency, (13) authority, (14) social proof, (15) scarcity, (16) and liking (17)--and they are not fully functional for lawyers seeking to persuade jurors and judges.

   PFEL is similarly laudatory in its assessments of the rules that channel and limit evidence of a person's character (or traits of character). In developing this doctrine (which continues to befuddle courts that must apply it), "rulemakers had latched onto some notions that are even more sound than they ever realized" (p. 29). "[T]he law's doubts about the usefulness of the concepts of character and personality are on the correct track psychologically. As to habit, from the perspective of psychological research and theory, the law is even more on target" (pp. 166-67).

   PFEL also has much to say about jurors' abilities and performance on various tasks. The institution of multi-member juries fares well. "Twelve (or 8 or 6) heads are better than one" for many reasons, "including the averaging of information, the aggregation of information, the suppression of individual jurors' biases, and the necessity of engaging in System 2 deliberative reasoning" (p. 46). And "a substantial body of empirical research has found that, for the great majority of cases, the characteristics of the jurors make only a modest difference to the verdict, whereas the evidence and arguments presented at trial have the greatest impact." (18)

   Of course, jurors (and judges) have many limitations. Nobody (or at least no cross section of people) is a very good lie detector.

   Despite decades of research effort to maximize the accuracy of deception judgments, detection rates rarely budge. Professionals' judgments, interactants' judgments, judgments of high-stakes lies, judgments of unsanctioned lies, judgments made by long-term acquaintances--all reveal detection rates within a few points of 50%. [Are we ready to] accept the conclusion implied by the first 384 research samples--that to people who must judge deception in real time with no special aids, many lies are undetectable [?] (19) Moreover, "[w]hen it comes to direct assertions of confidence (e.g., 'I'm sure') ... the research shows that witness accuracy and witness confidence are generally not highly correlated. Jurors, however, place great stock in such assertions of confidence" (p. 133). Because "the actual value of the evidence and how jurors perceive the value of the evidence are far apart [,this] is [] an area begging for a rule" (p. 133).

   In other areas, however, the authors find the research insufficient to refine or modify the folk psychology of jurists and legislators. For example,

   [m]any, but not all, of the studies find that the mock jurors give less weight to the same testimony when presented as hearsay than when presented by the witness with personal knowledge .... The studies vary on the hearsay exception that the information falls under, the instructions of the judge to the mock jurors, whether there was deliberation by the mock jurors, whether an expert testified on the problems of hearsay evidence, etc. With so many variables and so few studies, the research is not rich or systematic enough to draw conclusions about specific hearsay exceptions.... ... Psychology research could do a lot more.... (pp. 188, 201) Moving outside the realm of assumptions and studies on jury performance, Saks and Spellman are also guarded in their conclusions. Thus, they write that

   [t]he policy rationale [for Rule 407 on the admissibility of proof of subsequent remedial measures] is that the law wants to encourage defendants to make repairs ... [but critics maintain that] citizens are unlikely to be aware of Rule 407, and if they are not aware of it, it is unlikely to affect their behavior, (p. 77) Yet the authors "are aware of no empirical research testing whether the rulemakers or the critics have the stronger behavioral argument" (p. 78). Indeed, PFEL suggests that direct psychological or sociological studies are unlikely to provide an answer to some of the law's empirical questions. For example, they note that

   [p]sychologists have not done much research on privileges, most likely because they are not amenable to experimental research.... [T]here is some survey research ... but it is doubtful that survey methodology could provide good reliable answers to most of the important questions about privileges. (pp. 140-41) I could continue describing the authors' many assessments and insights, but I would not want to steal all the punchlines. Suffice it to say that, in PFEL, two of the world's leading scholars and teachers of law and psychology (20) distill a huge body of information and present their own opinions across the wide landscape of trial rules, procedures, and players. (21)

2. EXCAVATING ONE CORNERSTONE

   The panoramic view of PFEL blurs some details, and a number of its comments leave subtleties unstated. (22) This Part examines PFEL's exposition of two foundational concepts in evidence: relevance and probative value. My objective is to dig more deeply into this corner of...