Statistical techniques for juror and jury research

Juror and jury research is a thriving area of investigation in legal psychology. The basic ANOVA and regression, well‐known by psychologists, are inappropriate for analysing many types of data from this area of research. This paper describes statistical techniques suitable for some of the main questions asked by jury researchers. First, we discuss how to examine manipulations that may affect levels of reasonable doubt and how to measure reasonable doubt using the coefficients estimated from a logistic regression. Second, we compare models designed for analysing the data like those which often arise in research where jurors first make categorical judgments (e.g., negligent or not, guilty or not) and then dependent on their response may make another judgment (e.g., award, punishment). We concentrate on zero‐inflated and hurdle models. Third, we examine how to take into account that jurors are part of a jury using multilevel modelling. We illustrate each of the techniques using software that can be downloaded for free from the Internet (the package R) and provide a web page that gives further details for running these analyses.     

Preparation of a Ytterbium‐tagged Gunshot Residue Standard for Quality Control in the Forensic Analysis of GSR

Preparation of a ytterbium‐tagged gunshot residue (GSR) reference standard for scanning electron microscopy and energy dispersive X‐ray spectroscopic (SEM‐EDS) microanalysis is reported. Two different chemical markers, ytterbium and neodymium, were evaluated by spiking the primers of 38 Special ammunition cartridges (no propellant, no projectile) and discharging them onto 12.7 mm diameter aluminum SEM pin stubs. Following SEM‐EDS microanalysis, the majority of tri‐component particles containing lead, barium, and antimony (PbBaSb) were successfully tagged with the chemical marker. Results demonstrate a primer spiked with 0.75% weight percent of ytterbium nitrate affords PbBaSb particles characteristic of GSR with a ytterbium inclusion efficiency of between 77% and 100%. Reproducibility of the method was verified, and durability of the ytterbium‐tagged tri‐component particles under repeated SEM‐EDS analysis was also tested. The ytterbium‐tagged PbBaSb particles impart synthetic traceability to a GSR reference standard and are suitable for analysis alongside case work samples, as a positive control for quality assurance purposes.     

Exploring the criminal histories of stranger sexual killers

Although sexual homicide is receiving increasing research attention, few studies have examined the criminal histories of sexual killers in any detail. This study examined the criminal histories of 81 British stranger sexual killers to determine whether they were generalist, specialists or both and whether their criminal histories reflected violent, sexual, marginality and over control pathways. Results found most stranger sexual killers were generalist offenders and sexual homicide was part of a varied criminal repertoire and non-sexual crimes predominate. This ‘antisocial orientation’ means future offending may not be limited to sexual violence. Criminal histories reflected the violent, sexual, marginality and over control pathways, but offenders in the violent pathway were more criminally orientated. The clinical and investigative implications of these findings were considered as they suggest knowledge of the criminal histories of stranger sexual killers is an important consideration for criminal justice professionals.