The effect of verdict system on juror decisions: a quantitative meta-analysis

Jackson, E., Curley, L., Leverick, F. and Lages, M. (2024) The effect of verdict system on juror decisions: a quantitative meta-analysis. Psychiatry, Psychology and Law, (doi: 10.1080/13218719.2023.2272912) (Early Online Publication)

Abstract

We study the effect of the Scottish three-verdict system (guilty, not guilty, not proven) and the Anglo-American two-verdict system (guilty, not guilty) on juror decisions by combining data sets from 10 mock trials reported in suitable studies. A logistic regression with random effects uses the exact number of convictions and acquittals in 10 mock trials from a total of 1778 jurors to reliably estimate the effect of verdict system. We found a statistically significant verdict effect suggesting that the odds for a conviction by a juror are about 0.6 times or 40% lower under the three-verdict system than under a conventional two-verdict system. Possible explanations and implications of this verdict effect are discussed. This finding helps to better understand juror decision making in the context of the current reform of the Scottish three-verdict system into a two-verdict system.

• Item Type: Articles
• Additional Information: This work was supported by the EU under Erasmus+ Grant QHELP 2019-1-EE01-KA203-051708.
• Keywords: Conviction rate, three-verdict system, two-verdict system, not-proven verdict, juror decisions, cognitive bias, logistic regression, random effects.
• Status: Early Online Publication
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Leverick, Professor Fiona and Jackson, Mrs Elaine and Lages, Dr Martin
• Authors: Jackson, E., Curley, L., Leverick, F., and Lages, M.
• College/School: College of Medical Veterinary and Life Sciences > School of Psychology & Neuroscience; College of Social Sciences > School of Law
• Journal Name: Psychiatry, Psychology and Law
• Publisher: Taylor and Francis
• ISSN: 1321-8719
• ISSN (Online): 1934-1687
• Published Online: 11 January 2024
• Copyright Holders: Copyright © 2024 The Author(s).
• First Published: First published in Psychiatry, Psychology and Law 2024
• Publisher Policy: Reproduced under a Creative Commons licence