Communication of Statistically Based Conclusions to Jurors-A Pilot Study

Abstract

During the 20th century, scientists in most forensic sub-disciplines reported categorical opinions on the source of material recovered in connection with a crime. Following the development of DNA evidence, legal and scientific scholars have urged these scientists to determine the probative value of forensic evidence in a more transparent way and to present conclusions in a fair and balanced fashion. Unfortunately, statistical information is not well understood or used rationally by most individuals when reasoning. Most jury studies have focused on jurors’ understanding of reporting techniques currently used by the profession; very few studies have attempted to develop novel reporting techniques based on cognitive-psychological findings on efficient communication. This study explores some possible reporting techniques and describes some of the main challenges of the development and testing of novel conclusion presentation methods. Some of our main findings are similar to other jury studies. Study participants did not entirely account for the forensic evidence when updating their belief that the considered source was in fact the true source of the trace, however, participants provided with likelihood ratios showed less variability in their answers compared to participants provided with categorical conclusions. In addition, we observed a systemic bias against the defendant prior to hearing the forensic evidence. Finally, we found that recording participants’ beliefs involved solving a circular conundrum: measuring the variability in the participants’ understanding of quantitative information requires the use of quantitative scales that they may not all perceive in the same way.

Publication
Journal of Forensic Identification, (66), 5, pp. 405–427
Date
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