Sex Offender Modus Operandi Stability and Relationship With Actuarial Risk Assessment

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Three studies conducted in Vermont yielded data on 82 sexual recidivists’ index offenses (Time 1) and sexual reoffenses (Time 2) across 16 modus operandi (MO) characteristics. The current study examines the stability of these 16 characteristics between Time 1 and Time 2 offenses. Probabilities of Time 1–Time 2 characteristic combinations are reported, including when controlling for static risk as measured by the Static-99R and Vermont Assessment of Sex Offender Risk–2 (VASOR-2). Overall, considerable stability of offenders’ MO was evident between Time 1 and Time 2 offenses. Victim characteristics and offense behaviors were the most stable MO characteristics, and degree of force used and victim injury were less stable and trended toward less forceful and less injurious reoffenses. Controlling for static risk had little impact on the patterns of MO stability.