By Karen Franklin, Ph.D.
Use of a controversial psychopathy test is skyrocketing in court, even as mounting evidence suggests that the prejudicial instrument is highly inaccurate in adversarial settings.
The latest study, published by six respected researchers in the influential journal Law and Human Behavior, explored the accuracy of the Psychopathy Checklist, or PCL-R, in Sexually Violent Predator cases around the United States.
The findings of poor reliability echo those of other recent studies in the United States, Canada and Europe, potentially heralding more admissibility challenges in court.
Although the PCL-R is used in capital cases, parole hearings and juvenile sentencing, by far its most widespread forensic use in the United States is in Sexually Violent Predator (SVP) cases, where it is primarily invoked by prosecution experts to argue that a person is at high risk for re-offense. Building on previous research, David DeMatteo of Drexel University and colleagues surveyed U.S. case law from 2005-2011 and located 214 cases from 19 states -- with California, Texas and Minnesota accounting for more than half of the total -- that documented use of the PCL-R in such proceedings.
To determine the reliability of the instrument, the researchers examined a subset of 29 cases in which the scores of multiple evaluators were reported. On average, scores reported by prosecution experts were about five points higher than those reported by defense-retained experts. This is a large and statistically significant difference that cannot be explained by chance.
Prosecution experts were far more likely to give scores of 30 or above, the cutoff for presumed psychopathy. Prosecution experts reported scores of 30 or above in almost half of the cases, whereas defense witnesses reported scores that high in less than 10 percent.