The effect of adjusted actuarial risk assessment on mock-jurors’ decisions in a sexual predator commitment proceeding

Twenty states and the federal government have adopted statutes that authorize the post-incarceration commitment of sexually violent predators. Actuarial risk assessment is commonly used, and in some states statutorily required, to assess the risk of sexual recidivism in these proceedings. Professionals sometimes modify actuarial risk estimates with their own clinical judgment, the so-called adjusted actuarial approach. Although this approach is controversial and courts almost uniformly permit it, the effect of this practice on fact finders is unknown. This experiment found that adjusting actuarial risk estimates affected mock-jurors’ decisions to commit a respondent, but only when the adjustment increased the risk estimate. Adjusting the risk estimate downwards did not decrease the commitment rate. Notably, this effect occurred without the expert providing any rationale for the adjustment. Further analyses suggest that participants engaged in motivated reasoning, which refers to the tendency to selectively credit or discredit information depending on whether it is congenial to the desired outcome. Participants who chose to commit the respondent deemed the assessment highly acceptable when it indicated high risk, and relatively unacceptable when it indicated low risk, even though the substance of the assessments was identical. Implications for the adjusted actuarial approach are discussed in conjunction with existing legal admissibility standards for expert testimony