Can experts remain objective and accurate when one particular side in adversarial legal proceedings retains them? Despite long-standing concerns from the legal system and the general public, research has only recently explored whether experts can provide opinions unbiased by the side that retained them. This review addresses some of the factors that may cause disagreements between opposing experts. After summarizing recent field and experimental studies on mental health evaluations by forensic experts, we conclude that working for one side in an adversarial case causes some experts' opinions to drift toward the party retaining their services, even on ostensibly objective instruments and procedures. We call this process adversarial allegiance. The mechanisms that underlie adversarial allegiance among forensic experts are likely similar to the unconscious heuristics and cognitive biases that compromise judgment in a variety of other settings, but these will require further study to understand, and ultimately reduce, adversarial allegiance.


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