Towards a guide to best practice in conducting actuarial risk assessments with sex offenders

Assessing the risk of further offending behavior by adult sexual perpetrators is highly relevant and important to professionals involved in public protection. Although recent progress in assessing risk in sexual offenders has established validity of actuarial measures, there continues to be some debate about application of these instruments. Increasingly forensic practitioners are being requested to give expert witness evidence in formal settings where actuarial risk estimates are being examined. This is true in the Sexually Violent Predator (SVP) hearings in the United States and the Parole Board Hearings in the United Kingdom. It is important therefore for practitioners using actuarial scales in adversarial settings to have a thorough understanding of methodological limitations of the technology and possible errors and inaccuracies of reporting actuarial risk estimates in individual cases. The aim of this paper is to summarize strengths and weaknesses of actuarial risk data, and to contribute to developing guidance on best practice when using actuarial measures in adversarial settings. This paper is organized into six areas: (1) Actuarial scales in practice; (2) Understanding risk prediction concepts; (3) Factors known to affect actuarial estimates; (4) Can we use group data to assess risk in individual cases; (5) Choosing which actuarial risk measure to use; and (6) Reporting actuarial risk estimates. It is hoped this paper goes someway to establishing guidance on the best practice of actuarial scales and associated limitations.