Psychologists at the University of Virginia and Sam Houston State University found that paid forensic experts are vulnerable to bias.  Their study reveals that forensic psychologists and psychiatrists who believed that they were consulting on a real case, interpreted evidence differently depending on whether they were being “hired” by the prosecution or defense.  Bias in psychologists hired to go to court could have an immense impact on defendants’ lives. In many cases, psychological evaluations influence decisions about what sentences people deserve.

The researchers decided to conduct a “real world” experiment, providing 118 experienced forensic psychiatrists and psychologists from several states the opportunity to participate in a two-day workshop covering the psychological tests used to evaluate sexually violent predators. In exchange, the experts agreed to provide paid consultation to a state agency that was supposedly reviewing a large batch of sexually violent offender case files.  In fact, the case files were real, but they weren’t working on the trial.  The researchers gave each of the forensic experts the same four cases (unbeknownst to them).  Half were told the prosecution hired them and half were told the defense hired them.  In this study, the cases the experts examined were for violent sexual offenders, whose sentences depend largely on their likelihood of reoffending.  The experts returned weeks later to meet with an actual attorney and score risk assessment instruments.

On average, in most measures, the defense-hired experts came to significantly different conclusions than the prosecution-hired ones.  Even though the experts used the same well-known risk assessment tools to evaluate the same people, their scores were different depending upon who hired them.  In other words, the “prosecution” consultants scored the offenders riskier then the “defense” consultants.

“Most expert witnesses believe they perform their job objectively. These findings suggest this may not be the case,” one of the researchers, Daniel Murrie of the University of Virginia, said in a statement.

We were surprised by how easy it was to find this ‘allegiance effect,'” says psychological scientist Murrie, “The justice system relies often on expert witnesses…”  Murrie and co-author Marcus Boccaccini at Sam Houston State have worked in forensic psychology for years, watching the adversarial justice system use forensic experts.  “We became increasingly curious about whether forensic psychologists and psychiatrists could actually do what their ethical codes prescribed: handling each case objectively…” said Murrie.

Murrie notes that most people in this line of work really do try to be objective, and not every expert in the study demonstrated bias.

“In short, even experts were vulnerable to the same biases as the rest of us, in ways that left them less objective than they thought,” says Murrie.

“Demonstrating that allegiance is a problem is the first step towards solving the problem,” Murrie concludes. “The justice system certainly needs the expertise experts can offer, but the system also needs to be able to trust that their input is truly objective.”


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