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Testing the Effects of Selected Jury Trial Innovations on Juries' Comprehension of DNA Evidence in New Castle County, Delaware, 2003 (ICPSR 4356)

Principal Investigator(s): Dann, B. Michael, National Institute of Justice; Hans, Valerie P., University of Delaware. Department of Sociology and Criminal Justice; Kaye, David H., Arizona State University. College of Law


This study tested whether the use of selected jury trial reforms enhanced jurors' understanding of complex and challenging scientific evidence presented during a criminal trial. The study examined the use of several jury reform techniques using a controlled mock jury approach in which mock juries composed of jury pool members watched a videotaped armed robbery trial featuring conflicting expert testimony about mitochondrial DNA (mtDNA) evidence. A total of 480 mock jurors were randomly assigned to eight-person juries and to one of the six conditions in the experiment. Ten mock juries were run in each of the six conditions (No Innovations, Note Taking, Question Asking and Note Taking, DNA Checklist and Note Taking, Jury Notebook and Note Taking, and All Innovations). At various points throughout the study (before the trial, after watching the videotaped trial, and after reaching a verdict), mock jurors were asked to complete questionnaires to gauge their understanding of mtDNA and the mtDNA evidence presented during the trial. They were also asked if and how the use of the jury trial innovations helped in their understanding of the mtDNA evidence. Specific variables contained in the study include demographic variables of the mock jurors, including their math and science background, mock jurors' views of science, their understanding of mtDNA, their perceptions of the reliability of different types of evidence, and the credibility of the prosecutor, defense attorney, detective, eyewitness, defendant, and expert witnesses, and whether the mock jurors favor or oppose the various innovations.

Access Notes

  • The public-use data files in this collection are available for access by the general public. Access does not require affiliation with an ICPSR member institution.


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Study Description


Dann, B. Michael, Valerie P. Hans, and David H. Kaye. TESTING THE EFFECTS OF SELECTED JURY TRIAL INNOVATIONS ON JURIES' COMPREHENSION OF DNA EVIDENCE IN NEW CASTLE COUNTY, DELAWARE, 2003. ICPSR04356-v1. Washington, DC: National Institute of Justice [producer], 2003. Ann Arbor, MI: Inter-university Consortium for Political and Social Research [distributor], 2006-01-06.

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This study was funded by:

  • United States Department of Justice. Office of Justice Programs. National Institute of Justice (2002-IJ-CX-0026)

Scope of Study

Subject Terms:   courtroom proceedings, DNA fingerprinting, juries, jury deliberations, jury instructions, reform, trial procedures

Smallest Geographic Unit:   none

Geographic Coverage:   Delaware, United States

Time Period:  

Date of Collection:  

  • 2003-10-14--2003-12-16 (October 14, 2003 through December 16, 2003)

Unit of Observation:   individual

Universe:   All jury-eligible adults called to jury duty at the New Castle County Courthouse in New Castle County, Delaware between October 14, 2003, and December 16, 2003.

Data Types:   survey data


Study Purpose:   The purpose of this study was to test whether the use of selected jury trial reforms enhanced jurors' understanding of complex and challenging scientific evidence presented during a criminal trial. This study combined the need for scientifically reliable data regarding the effects of jury trial reforms with the ongoing search for ways to improve juror understanding of DNA evidence. It was the first study of forensic evidence involving mitochondrial DNA (mtDNA) rather than nuclear DNA (nDNA).

Study Design:   In this experimental research study, 480 mock jurors were randomly assigned to eight-person juries and to one of the six conditions in the experiment. Ten mock juries were run in each of the following six conditions: Condition 1 -- No Innovations (Control), Condition 2 -- Note Taking (Control), Condition 3 -- Question Asking and Note Taking, Condition 4 -- DNA Checklist and Note Taking, Condition 5 -- Jury Notebook and Note Taking, and Condition 6 -- All Innovations (Note Taking, Question Asking, DNA Checklist, and Notebook). The checklist (Conditions 4 and 6) listed the principal questions about the mtDNA in the case, but left it for the jurors to fill in the answers. The notebook (Conditions 5 and 6) included background materials on the mtDNA issues. At the beginning of the study, demographic and background information were collected from the mock jurors as well as the participants' attitudes toward science in general and DNA evidence in particular. Then all 60 juries watched the same videotaped armed robbery trial. Rather than construct a mtDNA case from scratch, the mock trial was based on the issues, fact pattern, and transcripts of testimony from an actual trial, State v. Pappas. The nonscientific factual evidence was modified so that it was more ambiguous, making the mtDNA evidence more crucial to the jury's decision. The trial lasted 70 minutes, including one ten-minute break. In the two conditions in which questions for the experts were permitted (Conditions 3 and 6), the judge in the videotaped trial instructed the jurors on the procedure for asking questions of the expert witnesses. The research assistants repeated the instructions and invited questions after each of the scientific experts testified. If a juror had a question, he or she wrote the question on a sheet of note paper and turned it in to the research assistant. Judge Dann ruled on the admissibility of all questions. If the question was ruled admissible, Judge Dann or Professor Hans then called one of the DNA experts who had previously agreed to field calls and obtained a verbal response to the question. Judge Dann or Professor Hans wrote down the response verbatim and returned it to the jury at the next opportunity. Following the trial, but before jury deliberations, the mock jurors were asked to complete a second questionnaire that asked questions about the mtDNA and their use of and attitudes toward the jury reforms. There was a specific questionnaire for each condition, as items about the individual reforms differed from condition to condition. Once the mock jury had reached a unanimous verdict or had a mistrial declared because of a hung jury, all participants completed a third questionnaire. The mock jurors were asked about their reaction to the jury's verdict, their own individual views, mtDNA questions, and support for different jury reforms. A set of questions was added to this final questionnaire after a highly publicized mtDNA evidentiary hearing that occurred during the study, to determine participants' exposure to the hearing and any impact it may have had.

Sample:   Participants in this study were volunteers randomly selected from the pool of potential jurors who were not needed for actual trials. The source list for potential jurors in New Castle County, Delaware is the current list of the county's registered voters, drivers' license and identification card holders. A total of 3,381 jurors reported for jury duty during the period of the study, from October 14, 2003, through December 16, 2003. On some days, very few or no cases went to jury trial, and the volunteers never went through the jury selection process. On other days, most of the remaining jurors had gone through at least one jury selection and had not been selected. Once the need for actual jurors was met, staff members randomly selected a set of jurors from their master list of the remaining jurors who had previously volunteered for the mock jury study. On most days, there were 16 volunteers who were randomly divided into two groups of mock jurors. The overall nature of the study was then described to the jurors, who were given consent forms and were able to ask any questions about the study prior to agreeing to participate.

Weight:   none

Mode of Data Collection:   on-site questionnaire

Data Source:

Data for this study were collected from investigator administered questionnaires.

Description of Variables:   Variables found in this study include demographic variables of the mock jurors, such as age, gender, race/ethnicity, level of education, number of math and science courses taken in high school and college, job experience in math or science, current job status, job category, political views, household income, and if the mock jurors had ever served on a jury for a criminal or civil case. They were also asked questions to judge their knowledge and understanding of mtDNA and the mtDNA evidence presented in the trial, as well as question about their general views of science. Mock jurors were asked to rate the reliability of police evidence, victim evidence, expert evidence, DNA evidence, and eyewitness evidence. They were also asked to rate the credibility and believability of the prosecutor, eyewitness, detective, the prosecutor's expert witness, defense attorney, the defense attorney's expert witness, and the defendant. Mock jurors were asked whether or not they used the innovations available to them in their specific condition and why they had decided to use the innovation or not. Finally, the mock jurors were asked whether they favor or opposed the use of each innovation, regardless if it had been available for their personal use in the study.

Response Rates:   Between October 14, 2003, and December 16, 2003, a total of 3,381 jurors reported for jury duty. The volunteer rate was assessed on four separate days by calculating the proportion of volunteers to the total number of jurors present. The volunteer rate was an average of 74 percent, ranging from a low of 64 percent to a high of 97 percent.

Presence of Common Scales:   Several Likert-type scales were used.

Extent of Processing:  ICPSR data undergo a confidentiality review and are altered when necessary to limit the risk of disclosure. ICPSR also routinely creates ready-to-go data files along with setups in the major statistical software formats as well as standard codebooks to accompany the data. In addition to these procedures, ICPSR performed the following processing steps for this data collection:

  • Checked for undocumented or out-of-range codes.


Original ICPSR Release:   2006-01-06

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