Introduction and validation of the Juror Decision Scale (JDS): an empirical investigation of the Story Model

Purpose: To develop and validate a self-report measure of individual juror decision making within criminal trials, based on theoretical features set out in the Story Model of juror decision making.
Methods: The Juror Decision Scale (JDS) and Acceptance of Modern Myths about Sexual Aggression (AMMSA) measure were completed by 324 jury-eligible participants split across 27 jury panels, after observing a rape trial re-enactment high in ecological validity. Dimensionality and construct validity of the JDS was investigated using traditional confirmatory factor analysis (CFA) techniques alongside confirmatory bifactor analysis at two time points (individual juror
verdict decisions pre- and post-deliberation). Three competing models of the JDS were specified and tested using Mplus with maximum likelihood robust estimation.
Results: Bifactor model with three meaningful factors (complainant believability, defendant believability, decision confidence) was the best fit for the data at both decision points. Good composite reliability and differential predictive validity were observed for the three JDS subscales.
Conclusion: Alongside demonstrating its multidimensional conceptualisation, the JDS development permits future empirical testing of the Story Model theoretical assertions surrounding juror decision making. Present findings also provide early evidence of a certainty principle assessment process governing individual verdict decision formation. Theoretical and practical applications are discussed.