Matching offenders to appropriate services-the responsivity principle-is a key to successful supervision. The match should be based on two key concepts: the likelihood that the offender will continue to engage in criminal activities (risk) and the criminogenic needs that lead to criminal activities (needs). Offenders should receive services that address both risk and need factors.

Risk assessment tools can be used to identify individual offender factors known to impact recidivism -such as prior criminal record, incarceration history, age at first arrest, and nature of criminal conduct. These are all static factors, descriptors of an individual's prior history. Risk can be reduced through external controls to monitor the behavior of the offender, such as contacts, drug tests, electronic monitoring, curfew restrictions and service requirements. In general, the more risk factors an offender exhibits, the greater the level of external control. Offenders with a high recidivism risk benefit from more external control, but research indicates that offenders with a low risk of recidivism actually re-offend at a higher rate when they are placed under more supervision contacts. Intensive supervision services therefore should be devoted to higher risk offenders.