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Are forensic experts biased by the side that retained them?
Daniel C Murrie1, Marcus T Boccaccini, Lucy A Guarnera
11Institute of Law, Psychiatry, and Public Policy, University of Virginia.
Psychological Science
|August 24, 2013
Summary
Forensic experts showed bias in adversarial legal cases. Those working for the prosecution gave higher offender risk scores, while defense-retained experts gave lower scores, revealing an allegiance effect.
Area of Science:
- Forensic Psychology
- Legal Psychology
- Expert Witness Testimony
Background:
- Concerns exist regarding forensic expert objectivity in adversarial legal proceedings.
- The influence of legal party retention on expert opinions remains under-researched.
- Understanding potential biases is crucial for legal system integrity.
Purpose of the Study:
- To investigate the objectivity of forensic experts (psychologists and psychiatrists) when retained by opposing legal sides.
- To determine if an expert's allegiance to the prosecution or defense influences their risk assessments.
- To quantify the extent of potential bias, known as the allegiance effect.
Main Methods:
- 108 forensic psychologists and psychiatrists were recruited and compensated.
- Participants reviewed identical offender case files.
- Experts were deceptively assigned to either 'prosecution' or 'defense' consulting roles.
- Offender risk was assessed using two standardized risk-assessment instruments.
Main Results:
- Experts believing they worked for the prosecution assigned significantly higher offender risk scores.
- Experts believing they worked for the defense assigned significantly lower offender risk scores.
- Observed effect sizes (d) for this allegiance effect reached up to 0.85.
Conclusions:
- The study provides strong evidence for an allegiance effect in forensic experts within adversarial legal contexts.
- Expert opinions on offender risk can be influenced by the party that retains their services.
- This bias may impact the fairness and reliability of expert testimony in legal proceedings.
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