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Which Pedophiles Strike Again?Check the actuarial tables.

By Daniel Engber
Posted Thursday, July 14, 2005, at 6:16 PM ET
Duncan was likely to re-offend. Click image to expand.

On Wednesday, convicted sex offender Joseph Edward Duncan was charged with kidnapping two small children and murdering their older brother, their mother, and her boyfriend. When he was an inmate in 1999 and 2000, forensic psychologists evaluated Duncan using two different tests; both indicated he was likely to carry out a crime after being released from prison. How do psychologists assess the risk that a sex offender will strike again?

Through a combination of clinical judgment and statistics. A forensic psychologist interviews the convict, speaks with his family, and reviews police reports and prison records. The psychologist combines this research with actuarial assessments designed to predict whether an offender will commit another crime.

These actuarial tools have become common only in the past 10 years; today, most forensic psychologists recognize their value in predicting recidivism. Researchers design the assessments by examining sex offender databases. They look for the variables that best correlate with repeated criminal activity, then whittle these down to the most important factors.

The simplest tool for evaluating sex offenders is the Rapid Risk Assessment for Sex Offense Recidivism. The RRASOR (pronounced "razor") includes just four items. A sex offender gets one point for being under the age of 25 at the time of his release from prison, another if any of his victims were male, and a third if he wasn't related to his victims. He gets up to three more points depending on how many sex crimes he's been charged with. The most dangerous offenders, then, are young adults who have committed multiple sex crimes against boys they've never met before. According to the RRASOR's table of probabilities, these six-point cases have more than a 73 percent chance of committing another crime within 10 years. (Psychologists did use the RRASOR to assess Duncan, and found he was likely to strike again. He'd have received at least two points: His earlier victim was male and a stranger.)

More complex actuarial tools might grant points for antisocial behavior as an adolescent, a history of drug addiction, or specific details about the crime (like whether it occurred in a public place and the age of the victims). The Sex Offender Risk Appraisal Guide, for one, considers the offender's developmental history—for instance, whether he was separated from his parents at an early age—as well as any psychopathy and personality disorders he might have.

Critics of the actuarial approach say these tools are mostly based on "static" factors; they don't account for how risk changes over time. An offender who admits he has a problem and swears he'll change might be less likely to fall into old patterns than someone who's unapologetic about his crimes.

Hybrid evaluations have emerged in the past few years that incorporate dynamic factors. Psychologists who use the HCR-20 assessment look at the offender's criminal history, then add points based on clinical judgments—how impulsive or stressed out he is, for example, and how well he has responded to treatment.

Next question?

Explainer thanks Tom Kucharski of the John Jay College of Criminal Justice.

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Daniel Engber is an associate editor at Slate. He can be reached at .
Photograph of Joseph Edward Duncan by Jeff T. Green/Getty Images.
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