January 5, 2014

New evidence of psychopathy test's poor accuracy in court

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.

Looking at interrater reliability another way, the researchers applied a classification scheme from the PCL-R manual in which scores are divided into five discreet categories, from “very low” (0-8) to “very high” (33-40). In almost half of the cases, the scores given by two evaluators fell into different categories; in about one out of five cases the scores were an astonishing two or more categories apart (e.g., “very high” versus “moderate” psychopathy). 

Surprisingly, interrater agreement was even worse among evaluators retained by the same side than among opposing experts, suggesting that the instrument’s inaccuracy is not solely due to what has been dubbed adversarial (or partisan) allegiance.

Despite its poor accuracy, the PCL-R is extremely influential in legal decision-making. The concept of psychopathy is superficially compelling in our current era of mass incarceration, and the instrument's popularity shows no sign of waning. 

Earlier this year, forensic psychologist Laura Guy and colleagues reported on its power in parole decision-making in California. The state now requires government evaluators to use the PCL-R in parole fitness evaluations for “lifers,” or prisoners sentenced to indeterminate terms of up to life in prison. Surveying several thousand cases, the researchers found that PCL-R scores were a strong predictor of release decisions by the Parole Board, with those granted parole scoring an average of about five points lower than those denied for parole. Having just conducted one such evaluation, I was struck by the frightening fact – alluded to by DeMatteo and colleagues -- that the chance assignment of an evaluator who typically gives high scores on the PCL-R “might quite literally mean the difference between an offender remaining in prison versus being released back into the community.”

Previous research has established that Factor 1 of the two-factor instrument – the factor measuring characterological traits such as manipulativeness, glibness and superficial charm – is especially prone to error in forensic settings. This is not surprising, as traits such as “glibness” are somewhat in the eye of the beholder and not objectively measurable. Yet, the authors assert, “it is exactly these traits that seem to have the most impact” on judges and juries.

Apart from the issue of poor reliability, the authors questioned the widespread use of the PCL-R as evidence of impaired volitional control, an element required for civil commitment in SVP cases. They labeled as “ironic, if not downright contradictory” the fact that psychopathy is often touted in traditional criminal responsibility (or insanity) cases as evidence of badness as opposed to mental illness, yet in SVP cases it magically transforms into evidence of a major mental disorder that interferes with self-control. 

The evidence is in: The Psychopathy Checklist-Revised is too inaccurate in applied settings to be relied upon in legal decision-making. With consistent findings of abysmal interrater reliability, its prejudicial impact clearly outweighs any probative value. However, the gatekeepers are not guarding the gates. So long as judges and attorneys ignore this growing body of empirical research, prejudicial opinions will continue to be cloaked in a false veneer of science, contributing to unjust outcomes.

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The study is: 

The Role and Reliability of the Psychopathy Checklist-Revised in U.S. Sexually Violent Predator Evaluations: A Case Law Survey by DeMatteo, D., Edens, J. F., Galloway, M., Cox, J., Toney Smith, S. and Formon, D. (2013). Law and Human Behavior

Copies may be requested from the first author (HERE).

The same research team has just published a parallel study in Psychology, Public Policy and Law

“Investigating the Role of the Psychopathy Checklist-Revised in United States Case Law” by DeMatteo, David; Edens, John F.; Galloway, Meghann; Cox, Jennifer; Smith, Shannon Toney; Koller, Julie Present; Bersoff, Benjamin

My related essays and blog posts (I especially recommend the three marked with asterisks):

(c) Copyright Karen Franklin 2013 - All rights reserved

1 comment:

Roy Aranda said...

The ominous comment that, "So long as judges and attorneys ignore this growing body of empirical research, prejudicial opinions will continue to be cloaked in a false veneer of science, contributing to unjust outcomes", provides an alarming indication that pretextuality not only thrives, but festers in the SVP industry.

Roy Aranda, Psy.D., J.D.