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Deliberating science: Juries, scientific evidence and commonsense justice

Dissertation
Author: Erin Jennifer Farley
Abstract:
Prior empirical research examining how jurors use scientific evidence has largely relied upon a mathematical model of juror decision-making. This prior research suggests jurors are confused by probabilistic testimony and have a tendency to undervalue scientific evidence. Breaking away from the mathematical model tradition, this research utilized data from a project involving jury-eligible adults from Delaware to further examine how jurors evaluate and use statistical scientific evidence. This research project offered the unique opportunity to utilize jury deliberations as a window on lay views of science. Quantitative and qualitative analysis of questionnaire data and jury deliberations revealed a complex process in which jurors actively evaluated the scientific evidence. The most influential factor for evaluating mtDNA evidence was prior knowledge of nuclear DNA and to a lesser extent a variety of lay expectations, prior knowledge, and media exposure. Jurors had diverse expectations and evaluations of the scientific evidence. However, their individual verdict preferences and final jury verdicts were not based solely on reactions to the scientific evidence. Instead jurors' evaluations of scientific evidence interacted with their evaluations and expectations of non-scientific evidence while reflecting the constraints of the legal standards. Throughout the deliberation process, jurors called upon their notions of commonsense justice to guide them on what is just and fair.

TABLE OF CONTENTS

List of Tables……………………………………………………………..................viii List of Figures……………………………………………………….................……...ix Abstract…………………………………………………...............................................x

Chapter:

1 INTRODUCTION..............................................................................................1

2 SCIENCE IN THE COURTROOM...................................................................6

2.1 The Introduction of DNA into the Legal System......................................6 2.2 Scientific Evidence and the Law.............................................................12 2.3 DNA as Criminal Justice Tool................................................................15

3 JUROR COMPREHENSION OF SCIENCE AND TECHNOLOGY.............19

3.1 Lay Comprehension of Science and Technology...................................20 3.2 Lay Decision-Makers and Complex Scientific Evidence ......................24

4 JURORS, COMMONSENSE JUSTICE AND THE DELIBERATION PROCESS………………….............................………………………………51

4.1 Current Research Project and Structure of Dissertation.........................61 4.1.1 Research Hypotheses.................................................................65

5 METHODOLOGY……………………………………...................................67

5.1 Data Collection………………………...........…………………………68 5.2 Mock Trial Details……………...............……………………………...70 5.3 Participant Characteristics…………......................................................77 5.4 Measurement Variables for Chapter 6…………………………………78

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5.4.1 Dependent Variables……………...............……………………78 5.4.2 Independent Variables……………............……………………80 5.5 Measurement Variables for Chapter 9…………………........................82 5.5.1 Dependent Variables……………...............……………………82 5.5.2 Independent Variables……………............……………………82 5.6 Analysis Strategy…………………........................................................83

6 QUANTITATIVE ANALYSIS OF SURVEY MEASURES..........................89

6.1 Introduction.............................................................................................89 6.2 Prior Beliefs about Science, Technology, and Trial Evidence...............90 6.3 Perceptions of Police, Courts, Crime in the Local Community..............95 6.4 Perceptions of Mitochondrial DNA Evidence........................................99 6.5 Linear Regression Analysis..................................................................105 6.6 Conclusion............................................................................................109

7 AN EXAMINATION OF HOW JURORS DISCUSS AND EVALUATE MITOCHONDRIAL DNA.......................................................112

7.1 Introduction...........................................................................................112 7.2 Jury Deliberation: Scientific Evidence Discussion Content.................112 7.3 Will the Real DNA Please Stand Up! Evaluation of “New Technology”………………................................................................117 7.4 Strengths and Usefulness of Mitochondrial DNA Evidence................126 7.5 Heteroplasmy........................................................................................129 7.6 Contamination.......................................................................................131 7.7 Conclusion............................................................................................134

8 BEYOND BAYESIAN THEORY: A QUALITATIVE ANALYSIS ON THE INFLUENCE OF JUROR ERRORS AND LAY EXPECTATIONS...........................................................................................135

8.1 Introduction...........................................................................................135 8.2 Juror Use of Statistical Scientific Testimony and Related Errors.........138 8.2.1 Jurors use of Probabilities........................................................139 8.2.2 Jurors use of Frequencies.........................................................151 8.3 Lay Expectations & Evaluation of Contested Scientific Evidence.......162 8.4 Conclusion............................................................................................188

9 QUANTITATIVE ANALYSIS OF JUROR DELIBERATION....................192

9.1 Introduction...........................................................................................192 9.2 Crosstabulation Analysis......................................................................193 9.3 Logistic Regression Analysis Predicting Jury Final Verdict................194 9.4 Conclusion............................................................................................197

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vii 10 COMMONSENSE JUSTICE: NAVIGATING LAW AND SCIENCE........198

10.1 Introduction.........................................................................................198 10.2 Evaluation of Non-Scientific Evidence..............................................200 10.2.1 Evaluating of the Defendant.................................................200 10.2.2 Defendant as Liar v. Defendant as Nervous Kid..................202 10.2.3 Defendant as “Young and Stupid Kid”.................................203 10.2.4 Bank Teller as the “Honest Witness”....................................206 10.2.5 Attorneys as the “Bad lawyers”............................................211 10.2.6 Jack Webb (Detective) as “The Police”.................................216 10.3 Subjective Perspective and Defendant evaluation..............................219 10.3.1 Juror as Hypothetical Defendant..........................................220 10.4 Integrating Scientific and Non-Scientific Evidence ..........................225 10.4.1 Integrating Evidence and Guilty Verdict Preferences...........225 10.4.2 Integrating Evidence: Out of How Many…?.........................235 10.4.3 Integrating Evidence and Not Guilty Verdict Preferences..........................................................................................237 10.5 The Burden of Proof and Attorney Responsibility..............................241 10.6 Integrating Perceptions of Trial Evidence with the Reasonable Doubt Standard………………...........................................................244 10.7 Commonsense Justice: The Gut versus The Evidence........................253 10.8 A Snapshot of Group Discussion of Trial Evidence and Reasonable Doubt……………….......................................................258 10.9 Conclusion..........................................................................................263

11 CONCLUSION...............................................................................................265

REFERENCES...........................................................................................................275

APPENDIX.................................................................................................................284

LIST OF TABLES

5.1 Descriptive Statistics for Chapter 6 Quantitative Analysis Variables…………….......................................................……………………81

5.2 Descriptive Statistics for Chapter 9 Quantitative Analysis variables…………...............................................................................……….83

6.1 Distribution of Science and Technology Perspectives…………......................92

6.2 Distribution of Perspectives on Five Types of Trial Evidence………….……93

6.3 Descriptive Statistics for Index Measures……….............................................94

6.4 Zero-Order Correlation of Initial Mock Juror Perception Variables………………...................................................................................96

6.5 Mock Jurors’ Confidence in Community Police and Courts and Perceptions of Community Crime……………................................................97

6.6 Mock Juror Reports of How Easy or Difficult it was to Follow Expert Testimony on mtDNA Evidence (Pre-Deliberation)…………………………99

6.7 Zero-Order Correlation Matrix of Mock Jurors’ Perceptions of mtDNA Evidence………….............................................................................……….100

6.8 Mock Jurors’ Reports on Ability to Understand mtDNA Evidence (Pre- Deliberation)…………...................................................................................101

6.9 Mock Jurors’ Perception of mtDNA Reliability (Post- Deliberation)…………...........................................................................……102

6.10 Mock Jurors’ Perception of mtDNA Contamination (Post- Deliberation)……….......................................................................................103

6.11 Linear Regression Results Predicting Jurors’ Negative Science and Technology Perceptions………………..........................................................106

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6.12 Linear Regression Results Predicting Jurors’ Comprehension of mtDNA Testimony……………...................................................................................107

6.13 Linear Regression Results Predicting Jurors’ Ability to Follow Expert Testimony About mtDNA Evidence………...................................................107

6.14 Linear Regression Results Predicting Jurors’ Perceptions of mtDNA Reliability………………................................................................................108

6.15 Linear Regression Results Predicting Jurors’ Perception of mtDNA Evidence Contamination…………….............................................................109

7.1 Results of Auto-Code and Guided Systematic Search for Juror Scientific Discussions……….........................................................................................114

9.1 Crosstabulation of Juror Discussion Evaluations by Final Jury Verdict……………….....................................................................................194

9.2 Zero-Order Correlation Matrix of Juror Discussion and Evaluation Variables……………….................................................................................195

9.3 Logistic Regression Analysis of Final Jury Verdict………………...............196

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LIST OF FIGURES

7.1 Mock Juror Combined Mentions of Scientific Evidence Topics………………......................................................................................115

x

ABSTRACT

Prior empirical research examining how jurors use scientific evidence has largely relied upon a mathematical model of juror decision-making. This prior research suggests jurors are confused by probabilistic testimony and have a tendency to undervalue scientific evidence. Breaking away from the mathematical model tradition, this research utilized data from a project involving jury-eligible adults from Delaware to further examine how jurors evaluate and use statistical scientific evidence. This research project offered the unique opportunity to utilize jury deliberations as a window on lay views of science. Quantitative and qualitative analysis of questionnaire data and jury deliberations revealed a complex process in which jurors actively evaluated the scientific evidence. The most influential factor for evaluating mtDNA evidence was prior knowledge of nuclear DNA and to a lesser extent a variety of lay expectations, prior knowledge, and media exposure. Jurors had diverse expectations and evaluations of the scientific evidence. However, their individual verdict preferences and final jury verdicts were not based solely on reactions to the scientific evidence. Instead jurors’ evaluations of scientific evidence interacted with their evaluations and expectations of non-scientific evidence while reflecting the constraints of the legal standards. Throughout the deliberation process, jurors called upon their notions of commonsense justice to guide them on what is just and fair.

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CHAPTER 1 INTRODUCTION

Jurors occupy an occasionally controversial position within the legal system. As lay people, jurors are expected to represent the voice of the community in their decision-making. However, “scientific issues permeate the law,” and with ever- increasing frequency, jurors in complex cases must navigate two bodies of authority: law and science (Saks, Faigman, Kaye, & Sanders, 2004, p. 3). The role of complex scientific evidence and its corresponding expert testimony is an increasingly important concern among many legal and academic actors. Since nuclear deoxyribonucleic acid (DNA) was first introduced as evidence into the U.S. courtroom in the mid-1980s, concerns have been raised about jurors’ ability to adequately comprehend the statistical testimony associated with it. Although the admissibility of DNA evidence has largely been settled, the increasing reliance on this type of scientific evidence has fueled the concern that lay persons are unable to adequately comprehend and use DNA and other forms of complex scientific evidence in determining guilt or innocence. Empirical research juries provide some reassurance. In general, jurors adequately comprehend expert evidence. However, they are often skeptical about such evidence and the expert witnesses who explain it (Hastie, Penrod, & Pennington, 1983; Ivkovic & Hans, 2003; Shuman & Champagne, 1997). Jurors are not passive

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receptors for information and are not easily overwhelmed by expert witnesses. On the contrary, research reveals they take their role very seriously and are critical of all types of evidence, including scientific evidence (Diamond, Capser, & Ostergren, 1989; Vidmar & Diamond, 2001; Vidmar & Schuller, 1989). However, research also reveals that jurors may struggle to understand the statistical information associated with complex scientific evidence (Faigman & Baglioni, 1988; Lindsey, Hertwig, & Gigerenzer, 2003; Smith, Penrod, Otto, & Park, 1996; Thompson, 1989; Thompson & Schumann, 1987). As the reliance on forensic DNA testing is increasing within the criminal justice system, a number of pressing questions need to be addressed: What do lay fact-finders think about DNA evidence? Do they trust it? What do jurors really think of DNA testing? How do jurors perceive DNA match evidence? How do they perceive DNA match evidence compared to other types of evidence? If jurors do not come to the jury room as blank slates, do their prior expectations and knowledge impact their perceptions of case-specific DNA evidence? Although the general reliance on forensic DNA testing by the criminal justice system may be increasing, it is important to also recognize that among the cases in which DNA evidence is collected, very few reach the trial stage. Instead, many cases are settled by the plea bargaining process before the trial date arrives. In fact, the presence of DNA evidence may facilitate plea bargaining. Empirical research on juror comprehension and use of statistics associated with scientific evidence (i.e., hair, blood, DNA) has largely relied upon a mathematical model of decision-making, Bayes’ Theorem, to describe juror reaction

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to the presentation of statistical scientific evidence. Research using Bayes’ Theorem has generally concluded that jurors have a tendency to undervalue statistical scientific evidence and this undervaluation is viewed as an indicator of juror confusion. This research may inform us how lay fact-finders struggle with statistics and also reveal the differential psychological impact of various presentation formats on jurors’ guilt estimates. However, any generalization to the real-life experiences of jurors is limited. For example, one criticism of mathematical decision-making models like Bayes’ Theorem is that it assumes that jurors make one global judgment of the defendant’s guilt (Hastie, 1993). In other words, jurors have one single guilt estimate and simply “update” this subjective probability with the presentation of new evidence. Also, Bayes’ Theorem loses explanatory power when one considers that jurors’ responsibilities are often viewed as multidimensional. Moreover, research has revealed that human behavior seldom follows the probability theory principles (Hastie, 1993). The motivating force for current research analysis was to break away from the mathematical decision-making model and to take a more descriptive and qualitative perspective towards examining lay-fact finders’ understanding, evaluation, and use of statistical scientific evidence. More specifically, this research utilizes a commonsense justice perspective to examine how mock jurors manage and integrate two bodies of authority - law and science - in evaluating scientific evidence. Commonsense justice is generally defined as what ordinary people perceive is fair and just (Finkel, 1995). In addition, commonsense justice posits that these just and fair perceptions are influenced by the notions and sentiments that a lay fact-finder

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may rely upon to judge the defendant and the law. It is the objective of this research to utilize a commonsense justice perspective to examine what mathematical decision- making models lump together in one global and uninformative probability of guilt estimate. In addition, this research expands upon prior empirical research on commonsense justice by exploring the notions and sentiments lay fact-finders may possess or express about contested scientific and statistical evidence. This dissertation research focuses particularly on the discussions of mock jurors, taking advantage of the fact that jury deliberation opens a window on lay conceptions of scientific and legal evidence. As fact-finders, jurors are supposed to combine their commonsense judgments and the moral climate of the community with evidence presented at trial in determining the truth (Finkel, 1995). The role of jurors is to represent the subjective and important voice of the community:

The jury’s competence, unlike that of the judge, rests partly on its ability to reflect perspectives, experiences, and values of the ordinary people in the community—not just the most common or typical community perspective, but the whole range of viewpoints. …Ideally, the knowledge, perspectives, and individual errors and biases are discovered and discarded, so that the final verdict is forged from a shared understanding of the case. …group deliberation forces people to realize that there are different ways of interpreting the same facts. (Ellsworth, 1989, pp. 205-206)

The goal of this research is to utilize quantitative and qualitative data and analysis methods to achieve a fuller understanding of how jurors evaluate statistical testimony associated with complex scientific evidence. Analysis of these data will reveal a complex picture of jurors’ decision-making. However, before doing this, one

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5 must understand what crime scene evidence, such as blood, hair and, most importantly, DNA, means to the legal system. Chapter 2 presents a review of the evolving role of this evidence in the legal system.

CHAPTER 2 SCIENCE IN THE COURTROOM

2.1 The Introduction of DNA into the Legal System

As science and technology develop, their corresponding roles in the legal system have become increasingly important in solving crimes and resolving legal questions. In criminal investigations, police have long relied on physical evidence gathered at a crime scene to help identify suspects and witnesses. For example, fingerprinting has been used for over 100 years to identify suspects, perpetrators and victims (Cole, 2001; Robertson & Vignaux, 1995). Blood-typing, hair-comparison, and handwriting analysis were other early “scientific” techniques used to help identify both victims and perpetrators. Most importantly, over the past two decades the use of DNA evidence has become a crucial factor in the courtroom. At the same time its presence remains quite controversial. Nuclear DNA is the blueprint for every individual, and it contains a double helix with sequences of “base pairs” (adenine, cytosine; guanine, thymine) that are unique to each individual. Nuclear DNA is located in the center of the cell nucleus and possesses 23 pairs of chromosomes (Adams, 2005). Each individual inherits 23 chromosomes from his or her mother and 23 chromosomes from his or her father.

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Because of its great discriminatory power, nuclear DNA, has the ability to identify specific individuals. Nuclear DNA can be collected from many sources, including blood, hair, semen, and saliva. In addition due to various technological advancements nuclear DNA can be successfully extracted from very small samples. Use of nuclear DNA in the legal system is popularly referred to as DNA fingerprinting, which references its ability, like fingerprinting, to identify any individual (Jeffreys, Wilson, & Thein, 1985). However, DNA analysis cannot identify identical twins, because they have identical nuclear DNA profiles. Ironically there is a more traditional way to differentiate between identical twins: fingerprinting. Although they possess identical nuclear DNA, identical twins do not possess the same fingerprints (Kobilinsky, Liotti, & Oeser-Sweat, 2005). At a crime scene, the collection of biological evidence that contains nuclear DNA, like hair or blood, can help identify the source of the evidence. The objective of testing biological substances is to link either the suspect or the victim to evidence collected at a crime scene. The first use of forensic DNA analysis in a criminal case occurred in 1985 in England (Kobilinsky et al., 2005; Michaud 1988). Using forensic DNA analysis, University of Leicester geneticist Alec Jeffreys helped assist police in Leicester, England to identify the individual who raped and murdered two girls. This case became infamous because the man originally taken into custody, who confessed to the murder of the second girl but denied being involved in the first murder, was excluded as a suspect when his nuclear DNA profile did not match that found on either victim. In addition, when the nuclear DNA samples found on the two girls were

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compared, Jeffrey’s analysis confirmed police officers’ suspicion that the same person had committed both murders. With nuclear DNA as their only strong lead, the police department, with the assistance of Jeffreys, undertook the incredible task of testing all the men who lived or worked in the area and who could have committed the murders. After collecting blood samples from 4,582 men and conducting DNA analysis on 500 who could not be excluded by standard blood typing, there was still no match (Aronson, 2005). The real perpetrator, Colin Pitchfork, had convinced a friend to submit his DNA in Pitchfork’s name. No one was the wiser. Only when this friend revealed what he had done in a bar conversation did the police became aware of Colin Pitchfork’s attempt to avoid submitting a DNA sample. When it was finally taken, his nuclear DNA matched samples taken from both crime scenes. Thus, Colin Pitchfork became the first murder suspect to be identified and convicted as a result of forensic DNA analysis (Kobilinsky et al., 2005). Although this case has been long heralded as the first successful use of nuclear DNA evidence, Colin Pitchfork’s prosecution resulted more from an old- fashioned tip than from forensic DNA analysis. After Colin Pitchfork was arrested, but before nuclear DNA testing was conducted, he confessed to both murders (Aronson, 2005). Soon after this famous case nuclear DNA began to show up in U.S. courts. In November of 1987 in Orlando, Florida, Tommie Lee Andrews became the first man in the United States whose conviction for rape was largely based on forensic nuclear DNA analysis (Michaud, 1988). Since 1987, the use of nuclear DNA evidence has

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significantly increased (Lee & Tinady, 2003). Presently, all 50 states possess nuclear DNA databases, which include DNA profiles from evidence left at a crime scenes where the perpetrator is unknown and also the DNA profiles of perpetrators convicted of various crimes (Lazer, 2004). The FBI also possesses a nuclear DNA database, the Combined DNA Index System (CODIS), which is compatible with international databases from Europe and South America so that criminals can be tracked and caught (Kobilinsky et al., 2005). Many legal actors and lay people are aware of nuclear DNA, its use in the legal system and its ability to identify victims and perpetrators of crimes. Besides the popularity of television crime dramas, a number of high profile criminal cases and extensively covered media events can take a bit of credit for that. For example, post- conviction exonerations have garnered a great deal of media attention, and nuclear DNA evidence was also a key aspect of the OJ Simpson trial, which became a six- month media extravaganza (Lazer, 2004). Although a large segment of the public may be aware of DNA in general, many may not know that there are actually two different types of DNA: Nuclear DNA and mitochondrial DNA. Within each cell, but outside the nucleus, are thousands of peanut-shaped structures called mitochondria (Adams, 2005). What makes mitochondrial DNA important to the criminal justice system is that when nuclear DNA has degraded due to decomposition, mitochondrial DNA can be extracted from skeletal remains. Also, unlike nuclear DNA, it can be extracted from very small degraded samples. However, mitochondrial DNA is maternally inherited, and it is significantly smaller than

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nuclear DNA, which means less variation in base pairs. Unlike nuclear DNA, mitochondrial DNA is not composed of half of the mother’s and half of the father’s DNA. As a result, mitochondrial DNA testing cannot uniquely identify an individual; it can only narrow identity to a group or population (Adams, 2005). A number of recent and highly publicized uses of mitochondrial DNA testing include identifying the skeletal remains of the Romanov family (Gill, Ivanov, Kimpton, Piercy, Benson, Tully, Evett, Hagelberg, & Sullivan, 1994), identifying the remains of the Vietnam Solider from the Tomb of Unknowns (Myers, 1998) and most recently the Laci Peterson murder investigation and the identification process of victims from the September 11 th terrorist attacks (Altman, 2001). Although mitochondrial DNA has been involved in a number of high profile cases its use in the courtroom is not as well established as the use of nuclear DNA. The first criminal case involving mitochondrial DNA (mtDNA) occurred in 1996. According to an article in the New York Times , the FBI had been working on mitochondrial DNA testing since 1990, and it officially implemented an mtDNA profile in Tennessee v. Ware (New Type of DNA Testing, 1996). In 1994, Paul Ware, then 27, was charged with the brutal rape and murder of a four-year old girl (Tennessee v. Ware, 1997). A number of hairs were collected from the crime scene and the victim’s body, including a hair found inside the victim’s pharynx. The FBI analyzed the hairs, and most importantly the hair found in the victim’s throat. At the time of the trial, the FBI’s mitochondrial DNA database consisted of 742 persons. The racial/ethnic makeup of the database consisted of 423 Caucasian and 319 African American/Black samples. Two specific areas of the

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mtDNA sample, the most variable, were extracted for analysis. Each of these “hyper variable” sections was roughly 300 base pairs long (Adams, 2005). The mtDNA profile drawn from the “unknown” hairs found at the crime scene were an exact match (on 600 bases) to the defendant’s mtDNA drawn from a saliva sample. Since mtDNA does not have the ability to identify individuals, Paul Ware could not be specifically identified. However, he could not be excluded as a possible contributor of the hairs either. These mtDNA findings in combination with other non-scientific evidence and testimony were presented to the jury. The defendant was found guilty of felony murder and two counts of child rape. On appeal, the defendant questioned “whether the results of mitochondrial DNA analysis were properly admitted to evidence” (Tennessee v. Ware, p. 2). The appellate court of criminal appeals of Tennessee upheld the trial court mtDNA findings, and his conviction was affirmed. Subsequently Ware appealed to the United States Supreme Court, which declined to review his case. The use of forensic mtDNA analysis in the courtroom was established. The standards for deciding the admissibility of scientific evidence have changed since nuclear DNA was admitted into evidence in the mid-1980s. The standards have also changed since mtDNA evidence was admitted into evidence in 1996. To comprehend a discussion on the use of scientific evidence within the legal system, one must be aware of the standards relied upon to decide what evidence is admissible and what evidence is not. The following section offers a brief historical overview of the standards for admitting scientific evidence.

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2.2 Scientific Evidence and the Law

The admissibility standards of scientific evidence and expert testimony are not a matter of first impression for the United States Supreme Court; the Court has dealt with these issues long before the advent of DNA analysis. Frye v. U.S. (1923) was the first case to evaluate the admissibility of scientific evidence. Prior to Frye, courts relied on the commercial-marketplace test as the standard for admitting scientific evidence and testimony. This test deferred to buyers and sellers within the marketplace. If the scientific product or technique was valuable to buyers within the marketplace, it was deemed legitimate and admissible. In Frye the defendant was charged with murder. In support of his innocence, he asked the court to admit a polygraph test or lie detector called the “systolic blood pressure deception test.” This test monitored respiration, blood pressure, and perspiration, and by measuring these bodily functions, it purportedly could detect whether individuals were lying or telling the truth (Kobilinsky et al., 2005). Frye was an unusual case because the product the defendant was attempting to admit was so new that it had no prior marketplace value. The Court rejected the defendant’s request and set a new standard for expert testimony and evidence. When dealing with novel scientific evidence the Court opinion stated that:

Just when a scientific principle or discovery crosses the line between the experimental and demonstratable stages is difficult to define. Somewhere in this twilight zone the evidential force of the principle must be recognized, and while the courts will go a long way in admitting expert testimony deduced from a well-recognized scientific

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principle or discovery, the thing from which the deduction is made must be sufficiently established to have gained general acceptance in the particular field in which it belongs. (Frye, p. 1014)

With this decision, Frye’s “general acceptance” test for admissibility replaced the commercial marketplace test. However, it wasn’t until the debates regarding the Federal Rules of Evidence in the 1970s that Frye became “fashionable” (Saks et al., 2004, p. 71). The United States Supreme Court did not address questions of whether the Federal Rules of Evidence superceded Frye’s “General Acceptance” test until 1993. Daubert v. Merrell Dow Pharmaceuticals Inc. (1993) was a toxic tort case in which defendants claimed a prescription drug, Bendectin, taken by two pregnant mothers caused serious birth defects in their children. The defendants attempted to admit numerous animal studies that purported to support the claim that the use of Bendectin by pregnant mothers contributed to birth defects. The Court ruled that the Federal Rules of Evidence superceded Frye’s “General Acceptance” test and it outlined four standards for evaluating scientific evidence: testability or falsifiability, known or potential error rates, peer review publication, and Frye’s “General Acceptance” test. By altering judges’ roles, Daubert significantly changed the way the legal system handled scientific evidence and testimony. Daubert gave judges the responsibility to evaluate the reliability of scientific evidence and testimony. Prior to Daubert, judges deferred to the field in which the scientific evidence was produced. If a technique or procedure was generally accepted within its field, it was admissible. Judges did not have to become familiar with the science to evaluate it. After Daubert,

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however, judges could no longer defer to scientists; they were now expected to become familiar with the methods and culture of science and were responsible for determining if scientific evidence and testimony was valid and reliable (Saks et al., 2004). Judges became the “gatekeepers” of the courtroom and they screened scientific evidence and testimony to ensure relevancy and reliability. Daubert is one case in a trilogy that expanded judges’ responsibilities. In, General Electric Co., v. Joiner (1997) the 37-year-old plaintiff was diagnosed with small-cell lung cancer. A longtime smoker with a family history of lung cancer, he claimed exposure to polychlorinated biphenlys (PCB’s) had “promoted” his lung cancer. For support, the defendant presented animal studies that purported to show a positive relationship between exposure to PCB’s and cancer. The district court decision to exclude this scientific evidence was reversed by the Eleventh Circuit. The United States Supreme Court, however, held that the Eleventh Circuit should have offered greater deference to the District Court when making decisions to exclude or include scientific evidence or testimony. This decision expanded the gatekeeping responsibilities of judges originally outlined in the Daubert decision. The third and final case in the trilogy, Kumho Tire Co. v. Carmichael (1999), once again expanded the judge’s role as gatekeeper. Kumho involved a vehicle accident. One passenger died and others were seriously injured. Survivors claimed the tire that blew and caused the accident was defective and they attempted to admit the testimony of a tire specialist who claimed that the tire failure resulted from a defect. The trial court ruled that his methodology failed to meet the Daubert criteria. However the Eleventh Circuit reversed this decision, stating that Daubert applies only

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to scientific evidence and testimony, not to the tire expert’s testimony, which was more experience-based. The Supreme Court also held that it was appropriate to “flexibly” apply Daubert’s four factors to technical or specialized knowledge. Although the Daubert Court stated that the Federal Rules of Evidence (later amended in 2000) superceded the Frye Test, state courts retain the authority to define the judge’s role differently. A number of states still rely on Frye or a combination of Daubert and Frye to evaluate scientific and non-scientific evidence and testimony. This results in varying and conflicting admissibility decisions among jurisdictions, within the same jurisdiction and even within the same court. As a result, scientific evidence that may be admitted in one jurisdiction may be excluded in another. This lack of consistency is one explanation for the continued controversy surrounding the use of scientific evidence and testimony.

Full document contains 310 pages
Abstract: Prior empirical research examining how jurors use scientific evidence has largely relied upon a mathematical model of juror decision-making. This prior research suggests jurors are confused by probabilistic testimony and have a tendency to undervalue scientific evidence. Breaking away from the mathematical model tradition, this research utilized data from a project involving jury-eligible adults from Delaware to further examine how jurors evaluate and use statistical scientific evidence. This research project offered the unique opportunity to utilize jury deliberations as a window on lay views of science. Quantitative and qualitative analysis of questionnaire data and jury deliberations revealed a complex process in which jurors actively evaluated the scientific evidence. The most influential factor for evaluating mtDNA evidence was prior knowledge of nuclear DNA and to a lesser extent a variety of lay expectations, prior knowledge, and media exposure. Jurors had diverse expectations and evaluations of the scientific evidence. However, their individual verdict preferences and final jury verdicts were not based solely on reactions to the scientific evidence. Instead jurors' evaluations of scientific evidence interacted with their evaluations and expectations of non-scientific evidence while reflecting the constraints of the legal standards. Throughout the deliberation process, jurors called upon their notions of commonsense justice to guide them on what is just and fair.