Three studies investigated lay people’s perceptions of the relative strength of various conclusions that a forensic scientist might present about whether two items (fingerprints, biological samples) have a common source. Lay participants made a series of judgments about which of two conclusions seemed stronger for proving the items had a common source. The data were fitted to Thurstone–Mosteller paired comparison models to obtain rank-ordered lists of the various statements and an indication of the perceived differences among them. The results reveal the perceived strength of several types of statements, relative to one another, including verbal statements regarding strength of support (e.g. ‘extremely strong support for same source’), source probability statements (e.g. ‘highly probable same source’), random match probabilities (e.g. RMP = 1 in 100 000), likelihood ratios, and categorical statements (e.g. ‘identification’). These comparisons in turn provide insight into whether particular statements about the strength of forensic evidence convey the intended meaning and will be interpreted in a manner that is justifiable and appropriate.
Perceived strength of forensic scientists’ reporting statements about source conclusions

Journal: Law, Probability & Risk
Published: 2018
Primary Author: William C. Thompson
Secondary Authors: Rebecca Hofstein Grady, Eria Lai, Hal S. Stern
Type: Publication
Research Area: Implementation and Practice
Related Resources
The Contribution of Forensic and Expert Evidence to DNA Exoneration Cases: An Interim Report
This report is from Simon A. Cole, Vanessa Meterko, Sarah Chu, Glinda Cooper, Jessica Weinstock Paredes, Maurice Possley, and Ken Otterbourg (2022), The Contribution of Forensic and Expert Evidence to…
CSAFE Project Update & ASCLD FRC Collaboration
This presentation highlighted CSAFE’s collaboration with the ASCLD FRC Collaboration Hub.
Understanding forensic decision-making with Item Response Theory: Using a NFI firearms study
This presentation is from the Forensic Big Data Colloquium at the Netherlands Forensic Institute, November 2022. Posted with permission of CSAFE.
An Ounce of Prevention: A Simple and Practical Tool for Mitigating Cognitive Bias in Forensic Decisions.
Learning Overview: The free information management toolkit described in this presentation will be introduced and attendees will learn to use this toolkit as a training tool and as a practical…