"Hired guns," "charlatans," and their "voodoo psychobabble": case law references to various forms of perceived bias among mental health expert witnesses.

Although in principle the legal system expects and professional ethics demand that expert witnesses be unbiased and objective in their forensic evaluations, anecdotal evidence suggests that accusations of financial bias, partisanship, and other forms of nonobjectivity are common. This descriptive survey of published legal cases expands on an earlier case law review (Mossman, 1999) attempting to encapsulate and summarize key issues concerning perceptions or allegations of bias in mental health expert witness testimony. Using a series of search terms reflecting various potential forms of accusatory bias, a total of 160 published civil and criminal court cases were identified in which 185 individuals (e.g., attorneys, trial and appellate judges, other witnesses) made one or more references to clinicians' alleged lack of neutrality. Allegations most typically involved describing the expert as having an opinion that was "for sale," or as a partisan or advocate for one side, although aspersions also were made concerning "junk science" testimony and comparing mental health experts to mystics and sorcerers. Our results indicate that diverse forms of bias that go beyond financial motives are alleged against mental health experts by various players in the legal system. Means are discussed by which experts can attempt to reduce the impact of such allegations.