Sex Offender Needs Assessment Rating

Now primarily of historical interest, the Sex Offender Needs Assessment Rating (SONAR) was the first focused attempt to assess change in sexual offenders based on dynamic risk factors. Dynamic risk factors are personal skill deficits, predilections, and learned behaviors correlated with sexual recidivism that can be changed through a process of “effortful intervention” (i.e., treatment or supervision). It was theorized that if such intervention reduced these risk-relevant factors, there would be a concomitant reduction in the likelihood that the offender would recidivate with another sexual crime. The SONAR demonstrated adequate internal consistency and a moderate ability to differentiate sexual recidivists from nonrecidivists (r = .43; ROC [receiver operating characteristic] area of .74).

As the 1990s drew to a close, the profession was making ever increasing use of actuarial risk assessments for sexual and violent offenders. The debate about the utility of such measures and their ability to reliably rank offenders according to risk of re-offense had, for the most part, been decided in favor of actuarial assessment. General acceptance of actuarial assess-ment grew as a number of tools (Violence Risk Appraisal Guide [VRAG], Sex Offender Risk Appraisal Guide [SORAG], Rapid Risk Assessment for Sexual Offense Recidivism [RRASOR], Minnesota Sex Offender Screening Tool-Revised [MnSOST-R], STATIC-99) gained acceptance in the courts and were used in most jurisdictions. However, those assessing risk in actual sexual offenders had no reliable technology for assessing change in risk status subsequent to treatment or other intervention. Actuarial measures, listed above, are based almost totally on the assessment of historical, nonchangeable (static) factors that are insensitive to clinical change. There had been previous attempts to measure dynamic or “changeable” factors, most notably in Don Andrews and Jim Bonta’s LSI-R; but prior to SONAR, there were no focused attempts to delineate changeable risk factors for individual types of crimes such as sexual crimes or violent crimes.

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Using a group of 409 sexual offenders on community supervision, the SONAR authors assessed by both file review and interview of the supervising community parole or probation officer the antecedents of sexual recidivism in a group of Canadian sexual offenders from nine Canadian provinces. Half of these sexual offenders had sexually recidivated while on community supervision, and half had not sexually recidivated while on community supervision. The sample was also roughly divided into equal numbers of incest offenders, child molesters, and rapists. Offenders were matched on offense history, type of index victim, and jurisdiction; nonrecidivists had an average of 24 months of supervision in the community, while recidivists had, on the whole, re-offended within 15 months. The interview and the file review sought data on 128 individual items from within 22 risk-relevant domains.

Comparison of these two groups of sexual offenders on this number of risk-relevant factors revealed a subset of those factors that were seen to change for the worse in the recidivistic group during the period of community supervision. Often, deterioration in the assessed areas of functioning preceded a sexual re-offense. These factors were divisible into two categories, each of which had an attending temporal association. Labeled Stable factors, the following five risk-relevant factors—intimacy deficits, social influences, antisocial attitudes, sexual self-regulation, and general self-regulation—seemed to be amenable to clinical intervention or treatment but on an intermediate term. These behavioral influences were seen as more “stable” in the personality and requiring sustained effort to change. The other four factors seemed to change on a much faster basis and to be a reaction to rapidly changing environmental stresses, conditions, or events. Labeled Acute risk factors, sub-stance abuse, negative mood, anger/hostility, and opportunities for victim access were seen as transient conditions that would only last hours or days. As such, these factors were seen as more strongly related to predicting the arrival of imminent re-offense. Statistical analysis provided a scale, showing moderate predictive accuracy, that was able to assess ongoing changes in risk in sexual offenders.

An important limitation of the study flows from this data having been collected retrospectively, with everyone involved knowing, a priori, the recidivism/nonrecidivism status of the offender. In addition, the same sample was used both to develop the instrument and to test it. The potential for retrospective recall bias, the retrospective nature of the study, and the lack of cross-validation called urgently for a truly prospective study of dynamic risk factors in sexual offenders.

Karl Hanson and Andrew Harris responded to these shortcomings, splitting the SONAR into two parts, manualizing the assessment, and expanding on the first 5 items of the SONAR to form the STABLE-2000 and the final 4 items of the SONAR to form the ACUTE-2000. The STABLE-2000 and ACUTE-2000 were subsequently tested in a truly prospective study using more than 1,000 sexual offenders on community supervision. Both tests showed predictive ability above that available to static assessment alone. That study led to the development of two new tests with even better predictive validity: the STABLE-2007 and the ACUTE-2007. These two measures have demonstrated predictive validity beyond that available to static assessment alone and beyond that of the SONAR and the STA-BLE-2000/ACUTE-2000 packages. The authors do not support or recommend the use of the SONAR but recommend the STABLE-2007 and ACUTE-2007, both available from the authors, for assessing dynamic changes in risk in sexual offenders.


  1. Hanson, R. K., & Harris, A. J. R. (2001). A structured approach to evaluating change among sexual offenders. Sexual Abuse: A Journal of Research and Treatment, 13(2), 105-122.
  2. Hanson, R. K., Harris, A. J. R., Scott, T.-L., & Helmus, L. (2007). Assessing the risk of sexual offenders on community supervision: The Dynamic Supervision Project (User report, Corrections research). Ottawa, ON, Canada: Public Safety Canada. Retrieved from

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