One depiction of the new Federal sentencing guidelines emphasizes that sentence length is a function of the offender's social characteristics, legal characteristics, offense characteristics, and the judge's predisposition. A close inspection of the equation reveals that the Sentencing Commission aims at crime reduction by relying upon collective incapacitation, i.e., imprisoning most offenders for a longer amount of time so they cannot commit crimes. The effectiveness of this strategy may be measured in terms of its immediate impact as well as its long-term influence on recidivism rates. An exact and precise evaluation of the sentencing reforms, however, awaits the resolution of several definitional and measurement problems associated with the use of recidivism as an outcome measure. These issues include whether recidivism is to be measured by rearrest, conviction, or reincarceration, and whether parole violations constitute recidivism. Another issue that must be addressed is the degree to which the length of time between release and recidivism is taken into account in assessing the strategy's effectiveness. Multiple indicators of recidivism should be used to reflect the broad and diverse legislative mandate given the Sentencing Commission. 2 tables.