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Individuals Convicted of a Sex Offense Who Are Monitored by GPS Found to Commit Fewer Crimes

An NIJ-sponsored research project examines the impact that GPS monitoring has on the recidivism rates of those committing sex offenses in California.
National Institute of Justice Journal
Date Published
February 26, 2013
Officer holding a monitoring device
Christopher Onstott (see reuse policy).

A study of people in California at high-risk for committing sex offenses while on parole found that those placed on GPS monitoring had significantly lower recidivism rates than those who received traditional supervision.

Researchers examined the effectiveness of using GPS to monitor persons at high-risk for committing sex offenses placed on parole in California. The NIJ-sponsored study included 516 high-risk persons on parole who had been released from prison between January 2006 and March 2009. Half of the people on parole who wore GPS monitoring devices in addition to receiving traditional parole supervision, which involves regular contact by parole agents and weekly treatment classes for those who had committed a sex offense ("GPS group"); the other half received only traditional parole supervision ("traditional group"). Researchers tracked each person on parole for one year following his initial parole date.

The study involved:

  • An outcome evaluation to assess both the cost of the GPS program and its effectiveness in reducing the criminal behavior of persons at high-risk for committing sex offenses while on parole.
  • A process evaluation to assess the program's design and implementation.

The researchers collected information from the state's data management system and examined official arrest records, parole supervision records, GPS monitoring data and state cost information. In addition, they conducted a survey of roughly 1,000 California Department of Corrections and Rehabilitation (CDCR) parole officers. The survey included questions about the GPS monitoring system, caseloads, program staffing and screening of persons at high-risk of committing sex offenses while on parole..

GPS More Expensive, but Also More Effective

The researchers found that those on parole in the traditional group — those not placed on GPS monitoring — committed new crimes and had their parole revoked more often than did those in the GPS group. In addition, the traditional group returned to custody at a rate 38 percent higher than the GPS group.

The cost analysis showed that in California, monitoring people on parole using GPS costs approximately $35.96 a day per person, while the cost of traditional supervision is about $27.45 a day. The GPS program is more expensive but more effective. Although the GPS program costs $8.51 more per day than traditional supervision, the GPS approach produced a decrease of 12 percentage points in arrests for any offense (from approximately 26 percent to 14 percent). In addition, individuals who were monitored using GPS complied with the terms of their parole at higher rates than did those on traditional parole.

The cost of California's GPS monitoring is lower than the cost of moving people on parole to "indefinite civil commitment," which entails sending those whose prison sentences are over, but who are believed to be too dangerous to release into the community, directly from confinement in prison to confinement in dedicated institutions. Such civil confinement programs can cost an average of more than $100,000 a year per person because of the programming that must be provided.


The researchers also examined the degree to which the GPS program delivered services as designed. Through a process evaluation that looked at responses from the survey of parole agents as well as GPS monitoring data, they found that CDCR had developed a protocol for the GPS program and largely followed that protocol while implementing the program. Based on their findings, the researchers made several recommendations.

Reexamine the identification of those at high-risk of committing a sex offense. To identify high-risk populations, California currently uses the standardized Static-99 risk instrument, which measures "static" factors that do not change over time (see related article, "Predicting Recidivism Risk: New Tool in Philadelphia Shows Great Promise"). However, in the survey of parole agents, nearly half of respondents said that the Static-99 does a poor job of identifying persons at high-risk for committing sex offenses. The researchers noted that the current risk instrument may predict recidivism, but those convicted of noncontact offenses such as exhibitionism pose less of a threat than do rapists and child molesters. Thus, the researchers recommend using a system that accounts for the different recidivism risks among those convicted of sex offenses and the varying threats to public safety.

Monitor attendance at treatment classes. CDCR mandates that persons at high-risk of committing sex offenses while on parole. attend weekly treatment classes. However, the researchers found a disconnect between parole agents and service providers in terms of tracking treatment attendance; 100 of them had no record of attending treatment during the study period. Further, in the survey of parole agents, only 75 percent of agents said that their charges attended treatment at least once a week. Previous research indicates that the meticulous monitoring of treatment is an important facet of supervision and that those convicted of sex offenses who stop attending treatment have higher recidivism rates. The researchers recommend that parole authorities strictly monitor and enforce weekly class attendance.

Use graduated sanctions that balance cost and risk. Instantly sending someone back to prison for a minor violation is costly. GPS supervision costs $35.96 daily, whereas the cost of keeping someone in a California prison is about $129 per day. The researchers recommend that CDCR — rather than issuing blanket parole revocations and sentencing violators to go back to prison for a few months at a time — employ a graduated sanctions system for dealing with parole violations. Such a system weighs the gravity of the offense against the need to preserve public safety, thereby increasing the likelihood that a person on parole with a serious violation is incarcerated, while one who presents less danger is still sanctioned but in a less restrictive, less costly manner (for example, by imposing a home curfew on the individual). The researchers added that California is in the process of piloting a new, structured decision-making system for dealing with parole violations, which will allow parole agents to scientifically weigh an individual's risk level and the benefits of alternatives to prison as part of their decision-making process.

Mandate the use of zones. The researchers also found that parole agents were neglecting to use inclusion and exclusion zones. Such zones are intended to keep those on parole either within certain areas, such as home and work, or away from certain places, such as schools or parks that attract many children. In the process evaluation, the researchers found that only 60 percent of parole officers always or often discussed the limits of inclusion zones, and only half discussed exclusion zone limits. The researchers argue that the use of zones may be the most important GPS tool because the application of zones allows parole officers to be alerted to the specific movements of the person convicted of a sex offense. Thus, they recommend making the zones compulsory.

Use a monitoring center to screen alerts. The large majority of parole agents (89 percent) reported in the survey that GPS monitoring was more time-intensive than traditional supervision. Until fairly recently, officers were receiving alerts when individuals tampered with the GPS device or committed other detectable violations. These alerts might also have included incidents such as an individual being in the basement of a building, sounding an "alarm" simply because someone was out of reach of the GPS monitoring system for a few minutes. From January 2009 until December 2010, paroled persons in California who had committed a sex offense generated 1.5 million alert notifications. The researchers noted that according to an internal CDCR document, officers spend 44 percent of their time monitoring movements by GPS and only 12 percent of their time in the field.

To help remove the burden on agents of responding to "minor" alerts, California switched to a centralized monitoring system in 2011. Under the new system, two vendor-operated centers screen the thousands of GPS alerts that agents receive each month and respond to the more technical alerts, such as a battery that has run too low. The centers forward alerts that are more serious to parole officers, allowing officers to focus more closely on direct supervision and on responding to real threats to community safety.

Limit caseload to 20. GPS increases the information that officers receive about people on parole, but reviewing this information is time-consuming and reduces the time available for direct supervision. As noted, agents spend only about 12 percent of their time in the field. According to the researchers, the best way to ensure that parole agents have sufficient time to directly supervise persons convicted of a sex offense is to limit the caseloads of GPS parole agents. In fact, the researchers found in their outcome evaluation that the size of the caseload was correlated with parole violations and with those on parole who are returning to custody. Therefore, the researchers recommend smaller caseloads of no more than 20 people per officer.

Issues and Concerns

Finally, the researchers noted that GPS monitoring is not a panacea. The systems can give false positives for violations. For example, sometimes a monitored individual "disappears" simply because he is in an underground location, forgets to recharge the battery that powers the system, or even decides to go to sleep under an electric blanket that disrupts the GPS signal. In these instances, the system would send an alert even though no criminal activity was taking place.

The researchers also pointed out other possible limitations of their work. The study lasted only a year, and results may vary over longer periods. In addition, at least one previous study found that once the GPS monitoring ends, those who had been monitored by GPS do just as poorly as the others.

Researchers at Development Services Group, Inc., of Bethesda, Md., and Old Dominion University in Norfolk, Va., conducted the study of persons on parole in California. Read their final report to NIJ, Monitoring High-Risk Sex Offenders With GPS Technology: An Evaluation of the California Supervision Program (pdf, 114 pages).

For More Information

NIJ Journal No. 271, February 2013
NCJ 240700

About This Article

This article appeared in NIJ Journal Issue 271, February 2013.

Date Published: February 26, 2013