A psychological assessment test often used to evaluate psychopathy in Canadian criminal cases is unreliable and prone to unconscious bias on the part of expert witnesses, according to research from the University of Toronto Mississauga.
Led by Rasmus Rosenberg Larsen, an assistant professor of forensic epistemology and philosophy of science at U of T Mississauga, the study examined 3,315 Canadian cases between 1980 and 2023, in which psychopathy assessments were used. The Hare Psychopathy Checklist-Revised, or PCL-R, was the most widely used tool, often by prosecutors.
The study, published in Psychology, Public Policy, and Law , found PCL-R scores differed depending on whether the expert witness was retained by the prosecution or defence, and that expert testimony often framed psychopathy as untreatable, contradicting the latest empirical research.
The results suggest that courts should exert caution when dealing with cases that use the PCL-R test, Larsen said.
"A psychopathy assessment can influence very high-stakes decisions," said Larsen. "The highest stake would be capital sentencing in the United States, for example; but there are also things like, say, parole. Does a person get to go home to see their family on a regular basis or not?"
Larsen noted courts use psychopathy tests to predict the likelihood of recidivism and advise judges on sentencing, parole eligibility, juvenile transfer to the adult system and civil commitment.
The study, supported by the Connaught Research Foundation, found use of psychopathy assessments increased by 858 per cent between 2000 and 2013. That was followed by a gradual decline of 63 per cent over the next decade.
Larsen said the decrease likely reflects growing concerns over the accuracy of testing results.
The PCL-R uses a 12- to 20-item checklist to generate scores between zero and 40. Scores above 25 are considered to indicate clinically significant levels of psychopathy.
"PCL-R was used like this magical tool where if you scored high, you could put that person in the bucket: the worst of the worst," said Larsen, who is cross-appointed to the department of philosophy in U of T's Faculty of Arts & Science. "It implies there's so many things wrong with (the accused) - they are high risk of recidivating and cannot be treated."
First published in 1980, the PCL-R manual has not been updated since 2003. Since the last revision, said Larsen, field research has found limited predictive value in PCL-R scores, especially when used on U.S.-based, male and/or minority populations.
The test's creator, Canadian forensic psychologist Robert Hare, is among the researchers who have cautioned against using the PCL-R test in court settings.
Hare warned that in order to be reliable, a PCL-R must be conducted by a professional with significant training and clinical experience, based on high-quality information and include ratings from two independent clinicians. In a 1998 article, Hare stressed that it is difficult to meet all those conditions in a court setting due to clinician scores being influenced by whether they were hired by the prosecution or the defence - a phenomenon called "adversarial allegiance."
"An expert witness is supposed to be independent, not swayed by who retained them," said Larsen. "However, this is exactly what we see."
Larsen added that he's seen swift assessments made based only on records and not interviews.
The PCL-R manual also describes psychopathy as an untreatable condition, a position generally dismissed by contemporary researchers after more recent studies showed that rehabilitation programs can have positive effects.
"We're using a tool that seems to only be harming people," Larsen said. "I know it is very hard for people to have sympathy because we're talking about people who have often done horrible things. But right is right, so we shouldn't be implementing a tool on a wrongful basis just because we want some sort of ends that cannot be justified."
Larsen cited a recent U.S. case in which a man was convicted of killing his own son and sentenced to death. "One of the reasons why he received the capital sentence was because of a PCL-R test," said Larsen. "Then, literally a day before his execution, the case was thrown out because later psychiatric assessments showed the person was just very autistic, but he had been ruled a 'psychopath.'"
Another concern, said Larsen, is that the assessments can create a stigmatizing effect on judges and jurors.
"When you call it a psychopathy test, you're triggering all sorts of biases because many people intuitively assume that when you say 'psychopath,' we're talking about the worst of the worst," he said. "The evidence does not suggest that, but this is nevertheless the semantic connotation of a label like that."
Larsen, who authored the book Psychopathy Unmasked: The Rise and Fall of a Dangerous Diagnosis, pointed to a mock trial experiment that found members of the public tend to associate psychopathy with much higher risk levels than is found in empirical research.
Their opinions are heavily influenced by movies, TV, documentaries and news programs, he said.
Larsen said he hopes the study will spark more conversations about the ethics of using PCL-R tests to advise court decisions.
"This isn't just intellectual debate - real people are impacted," he said. "We're talking about an industrial scale of misapplication and I think once we realize how big this problem is, we're going to be gasping."
