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NIJ
Journal No. 255 • November 2006
Can Jury Trial Innovations Improve Juror Understanding
of DNA Evidence?
by B. Michael Dann, Valerie P. Hans, and David H. Kaye
About the Authors
The Honorable B. Michael Dann (Ret.) was a Visiting Fellow
at the National Institute of Justice in 2004; Valerie P.
Hans is a Professor at Cornell Law School; and David H.
Kaye is a Regents’ Professor at Arizona State University
College of Law. University of Delaware doctoral candidates
Stephanie Albertson and Erin Farley assisted with the research
project.
A single spot of blood on a pink windowsill will tell investigators
who broke a windowpane, turned a lock, and kidnapped 2-year-old
Molly Evans from her bedroom in the middle of the night.
An expert witness will testify that the DNA profile of the
blood evidence recovered from the windowsill was entered
into CODIS, an electronic database of DNA profiles.[1]
That process yielded a “hit,” identifying the
defendant as the most likely source of the blood inside
Molly’s room.
But will jurors be able to understand the expert’s
intricate analysis and use it to reach a verdict? And whatif
anysteps can be taken to increase jurors’ comprehension
of complex DNA evidence?
Questions such as these prompted an NIJ-funded study on
the impact of jury trial innovations upon mock jurors’
understanding of contested mitochondrial DNA (mtDNA) evidence.
(See “How Mitochondrial
DNA Compares to Nuclear DNA.”) By examining how
jurors in different experimental conditions performed on
a Juror Comprehension Scale both before and after deliberations,
researchers were able to assess whether four specific innovations
improved jurors’ understanding of this complex evidence
and identify which innovations worked best.
Trial Innovations Tested
The four innovations used in the experiment were:
- Juror note taking. Mock jurors
were given a steno pad and pen for note taking and were
told that their notes would be available to them during
deliberations.
- Questions by jurors. Mock jurors
could submit questions to the presiding judge, who obtained
answers from an offsite DNA expert.
- Mitochondrial DNA (mtDNA) checklists.
This innovation guided jurors through complex mtDNA evidence
by asking them a series of questions. (See “mtDNA
Evidence Checklist.”)
- Multipurpose juror notebooks.
Mock jurors were given notebooks containing paper, copies
of the two experts’ slides, the mtDNA checklist,
a glossary of DNA terms used in the case, and a witness
list.
Selecting the Mock Jury
Jurors were selected from jury-eligible adults called to
jury duty in the Superior Court of New Castle County, Delaware.
Jurors were randomly assigned to 60 eight-person juries.
Each juror filled out an initial questionnaire that queried
his or her views on the reliability of certain types of
scientific testimony and about science in general. (See
“Mock Jurors’
Attitudes About Science and DNA.”)
Researchers then divided the juries into groups of 10 and
subjected each group to one of the following conditions:[2]
Experimental Condition |
Jury Innovations |
Condition 1 |
No innovations (control) |
Condition 2 |
Note taking |
Condition 3 |
Question asking and note taking |
Condition 4 |
DNA checklist and note taking |
Condition 5 |
Juror notebook and note taking |
Condition 6 |
All innovations (note taking, question asking, DNA
checklist, and juror notebook) |
The Mock Trial
The jurors then watched a videotape of an armed robbery
trial. Prosecutors presented the testimony of bank employees
who could not make a positive identification because the
robber wore a blue hooded sweatshirt and a partial mask.
However, one teller testified that she saw an unmistakable
inch-long, horizontal scar on the suspect’s cheek
when he wiped his face with his gloved hand.
Police searched the crime scene immediately after the robbery
and recovered a blue sweatshirt, a glove, and a small amount
of cash, including some of the “bait money.”[3]
Two human hairs recovered from the sweatshirt hood were
analyzed and found to match the defendant’s mtDNA.
No other physical evidence was recovered.
Jurors learned that an anonymous caller told police the
defendant had robbed the bank. Testimony established that
the defendant owned a blue hooded sweatshirt, had a scar
on his cheek, and had recently been seen flashing a large
roll of cash.
The defendant testified in his own defense and denied committing
the robbery. He told a detective that he had never been
in that bank and that he was at work when the robbery occurred.
He claimed that the excess cash was from a friend’s
recent repayment of a loan.
In an attempt to dispute the prosecution’s mtDNA
evidence, the defense introduced evidence that the defendant’s
wayward half-brother on his father’s side lived in
town at the time of the robbery. This fact, however, would
have been irrelevant to any juror who understood that mtDNA
is inherited only through the mother’s lineage. Researchers
made the rest of the circumstantial evidence purposefully
ambiguous so that jurors would feel compelled to consider
the mtDNA identification evidence and resolve the issues
raised by the prosecution and defense experts.
Expert Testimony on mtDNA
The prosecution’s expert testified that the mtDNA
profiles of hair from the sweatshirt and the samples combed
from the defendant’s head at the time of his police
interview were an exact match. He commented that the profile
was rare and had not been observed in the Federal Bureau
of Investigation’s (FBI’s) mtDNA database of
more than 5,000 samples. He added that 99.98 percent of
all Caucasian males would be excluded as potential contributors
of the two mtDNA samples. That meant that in addition to
other men in the same maternal line as the defendant, only
6 males in a population of 29,000 would have the same mtDNA
profile.
The defense expert agreed that the mtDNA samples matched,
but said that the FBI’s percentage of the population
excluded by the mtDNA evidence was too large because the
FBI failed to properly account for the possibility of “heteroplasmy”
in human hair. Heteroplasmy is a condition where some of
a person’s mtDNA exhibits a mutation and thus differs
(in at least one base pair) from the remainder of the person’s
mtDNA. By including heteroplasmic individuals as possible
sources of the hairs, the defense expert reduced the FBI’s
percentage of excluded males to 99.80 percent. She projected
that 57 males in the localityas opposed to the prosecution’s
estimate of 6could have been the source of the hairs.
After the videotape, jurors completed a second questionnaire
about their uses of and attitudes toward trial innovations.
They were then allowed to deliberate. Following the return
of a unanimous verdict or the declaration of a mistrial
(hung jury) in each case, jurors filled out a third and
final questionnaire.
Researchers then coded and analyzed jurors’ responses
to the questionnaires and reviewed the jurors’ written
notes, copies of the checklist, and notebook materials.
Questions posed by jurors during the trial were also analyzed.
All of the jury deliberations were videotaped, reviewed,
and coded to assess the use of jury innovations in group
deliberations.
Which Innovations Did Jurors Use?
The research showed that jurors used three of the innovations
the mostthe multipurpose notebook, note taking, and
the mtDNA checklist.
The multipurpose notebook was the most popular innovation:
92 percent of the jurors said that the notebooksin
particular, the expert’s slideshelped them to
remember and understand the case. The second most used innovation
was juror note taking: 88 percent of jurors took notes.
Two-thirds said their notes helped them remember the evidence.
The third most used innovation was the mtDNA checklist:
85 percent of jurors allowed to use the checklist said they
reviewed it during deliberations. Most found that the checklist
increased their understanding and recall of the evidence.
The least used innovation was jury questioning: only 22
percent of the jurors allowed to ask questions actually
did.
Which Innovations Enhanced Juror Understanding?
To see whether innovations improved juror understanding
of mtDNA evidence, researchers explored how jurors in the
different experimental conditions performed on Jury Comprehension
Scales[4] before and after
their deliberations, controlling for jurors’ educational
levels.[5] In general, researchers
found that jury deliberations improved jurors’ comprehension
of mtDNA.
Prior to deliberations, there were no significant differences
in how jurors who were assigned to the various conditionsthose
who used innovations and those who did notperformed
on the Juror Comprehension Scale. Even after deliberations,
comparisons of the responses of jurors given no innovations
(control group) with those who had them still showed no
significant differences in their understanding of mtDNA
evidence.
However, when the postdeliberation responses of jurors
allowed to use each particular innovation were compared
with the responses of jurors not allowed to use that innovation
(both those in the control group and those assigned another
innovation), differences emerged. Under this analysis, researchers
found that jurors allowed to use juror notebooks performed
significantly better on two aspects of the comprehension
testing (basic and expanded factual true-false tests) than
those not provided notebooks. Jurors provided with an mtDNA
checklist also performed better (on an expanded Jury Comprehension
Scale) than those without access to the checklist.
Researchers also examined whether actual usage of an innovation
improved juror understanding. The results were mixed. Data
showed that jurors who took advantage of two innovationsnote
taking and question askingdid not have higher levels
of comprehension; however, jurors who actually used the
mtDNA checklist and the juror notebook significantly outperformed
jurors who were afforded use of those innovations but declined
to use them.
There was also evidence that use of multiple innovations
improved juror comprehension. Using the note taking condition
as a control, researchers found that jurors allowed to take
notes and use a juror notebook did better on the Jury Comprehension
Scales postdeliberation than did those allowed only to take
notes. The same was true for jurors exposed to all four
innovationsthey also outperformed those jurors who
were only allowed to take notes. Thus, it appears that additional
innovations on top of jury note taking improves mock jurors’
comprehension of scientific mtDNA evidence.
Practical Suggestions for Practitioners
Based on the study, researchers believe that the use of
certain jury innovations has the potential to improve jurors’
comprehension of mtDNA and other scientific evidence. Methods
that provided direct guidance or additional expert informationsuch
as the mtDNA checklist and the juror notebookbest
improved juror understanding. This suggests that other jury
innovations that provide a better understanding of expert
evidence.such as juror tutorials in complex subjects and
court-appointed experts to discuss the parties’ often
conflicting scientific evidence.are ripe for evaluation.
The results of the study showed that most juries are capable
of comprehending and using different forms of DNA evidence
at trial. Nonetheless, researchers acknowledged that some
jurors are likely to have trouble with complex DNA evidence.
Researchers offered five ways to facilitate juror understanding
of DNA evidence:
- Distribute juror notebooks that contain
copies of the expert’s slides, overheads, and charts;
a glossary of technical terms; a list of the issues presented
by the DNA evidence; and blank paper for note taking.
- Distribute a checklist or inference
chart listing the issues presented by the DNA evidence
and provide a step-by-step pathway for the jurors’
resolution of those issues.
- Provide a brief, straightforward explanation
of forensic DNA without burdening jurors with nonessential
technical details about the analysis. Some deliberating
jurors complained about “technical overload”
of essentially uncontested matters.
- Allay fears of contaminationeven in
cases where there is no evidence it has occurred. A significant
number of jurors believed sample contamination was a problem
despite the total lack of evidence or argument by defense
counsel to suggest it occurred.
- Encourage jurors to weigh the probative
value of the DNA evidence linking the defendant to the
crime with the value of other nonscientific evidence.
Jurors attempt to combine both types of information to
arrive at an opinion regarding guilt, but are unsure how
to do so. Attorneys and experts should present simple,
understandable approaches to considering the value of
different types of evidence.
NCJ 215455
Sidebars
HOW MITOCHONDRIAL DNA COMPARES
TO NUCLEAR DNA
Nuclear DNA, or nDNA, is the genetic material inherited
from both parents (one-half from the mother and one-half
from the father). It is found in the nucleus of each
cell and is unique to each individual (except in cases
of identical twins). Nuclear DNA is a powerful identifier
and has been used for forensic purposes for decades.
Mitochondrial DNA (mtDNA)which is found in the
mitochondria of a cell, outside of the nucleus and
separate from nDNAis inherited solely from the
mother and is not unique. Everyone in the same maternal
line, for generations, will have the same mtDNA. Its
use as a forensic tool, in narrowing the pool of possible
donors of a sample, is a more recent development.
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mtDNA EVIDENCE CHECKLIST
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MOCK JURORS’ ATTITUDES
ABOUT SCIENCE AND DNA
Researchers found that the demographic profile (sex,
race, and age) of the 480 mock jurors bore striking
similarities to those of the entire pool of jury-eligible
adults. Most mock jurors had some science or mathematics
courses: on average, most had more than nine such
courses in high school or college. About half had
some job experience involving science or math.
Almost all (89 percent) of the mock jurors held positive
attitudes about science. However, a significant minority
expressed reservations about science. Negative attitudes
about the role of science in their lives were strongly
correlated with the level of formal education; jurors
with less education tended to express more negative
views.
Before the videotape was presented, researchers solicited
jurors’ views about DNA. Two-thirds of mock
jurors agreed that DNA evidence was “extremely
reliable.” Although half of the participants
had heard about mtDNA before this trial, most said
they had heard only a “small amount” about
it.
After the trial, however, almost all of the jurors
had a basic understanding of the mtDNA evidence. Solid
majorities of jurors (ranging from 66 to 90 percent)
exhibited correct understandings of most of the core
knowledge items about mtDNAe.g., where the mitochondria
are found in the cell, how samples are compared and
matches declared, and how mtDNA compares to nuclear
DNA.
Ninety percent of jurors correctly understood that
unlike nuclear DNA, mtDNA is inherited solely from
one’s mother. Those jurors rejected the defense
suggestion that the crime could have been committed
by the defendant’s wayward half-brother on his
fathers’ side, noting that the relationship
would not account for the presence of the defendant’s
mtDNA in the hair strands recovered from the hooded
sweatshirt.
On the other hand, some of the participants showed
a susceptibility to adversarial exaggerations and
misstatements about the scientific evidence:
- A number of jurors were persuaded by the prosecutor’s
argument that the likelihood of the defendant’s
innocence was equal to the percentage of Caucasian
males who could not be excluded as possible contributors
of DNA found on the hooded sweatshirt. Because the
prosecution’s expert estimated that 99.98
percent of Caucasian males would be excluded as
contributors, prosecutors argued that there was
only a .02 percent possibility that the defendant
did not commit the crime. This rationale erroneously
hinged the defendant’s guilt on one piece
of evidencehair found on a sweatshirt at the
scenewhile ignoring other circumstantial evidence
that was not directly incriminating.
- Some jurors also agreed with the defense attorney’s
questionable claim that the mtDNA evidence was entirely
worthless because people other than the defendant
could have contributed the hairs.
- One-quarter of the mock jurors thought that sample
contamination was “likely” despite the
absence of evidence or argument from either side
suggesting contamination of the hair samples or
the mtDNA.
As anticipated, the amount of formal education, the
number of courses in science and mathematics, and
some job experience involving science and mathematics
positively correlated with jurors’ correct understanding
of mtDNA.
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For More Information
- Dann, B.M., V.P. Hans, and D.H. Kaye,
Testing the Effects of Selected Jury Trial Innovations
on Juror Comprehension of Contested mtDNA Evidence,
final report submitted to the National Institute of Justice,
Washington, DC: August 2005 (NCJ 211000), available at www.ncjrs.gov/pdffiles1/nij/grants/211000.pdf.
Notes
[1] |
The Combined DNA Index System (CODIS)
is an electronic database of DNA profiles administered through
the Federal Bureau of Investigation. The system lets Federal,
State, and local crime labs share and compare DNA profiles.
Through CODIS, investigators match DNA from crime scenes
with convicted offenders and with other crime scenes using
computer software, just as fingerprints are matched through
automated fingerprint identification systems. CODIS primarily
uses two indexes: (1) the Convicted Offender Index, which
contains profiles of convicted offenders, and (2) the Forensic
Index, which contains profiles from crime scene evidence.
The strength of CODIS lies in solving cases that have no
suspects. If DNA evidence entered into CODIS matches someone
in the offender index, a warrant can be obtained authorizing
the collection of a sample from that offender to confirm
the match. If the offender’s DNA is in the Forensic
Index, the system allows investigatorseven in different
jurisdictionsto exchange information about their respective
cases. |
[2] |
Juror note taking was permitted in
all but the control condition because the more advanced
techniques (such as question asking and juror notebooks)
are unlikely to be offered by a court without the basic
reform of note taking. |
[3] |
Bait money is cash that tellers are
instructed to turn over in the event of a robbery. It contains
prerecorded serial numbers, enabling investigators to identify
the funds if recovered. |
[4] |
Researchers combined eight facts about
mtDNA to develop a Juror Comprehension Scale that measured
jurors’ understanding of mtDNA. |
[5] |
Researchers also controlled for juror
membership on a particular jury by using a “nested”
analysis. Because mock jurors in the study deliberated with
one another, jurors potentially influenced one another.
A nested analysis was used because juror’s responses
post-deliberation were no longer strictly independent observations.
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