Results indicate that between 6.2 and 14.1 offenses are prevented per year of juvenile incarceration and between 4.9 to 8.4 offenses are prevented per year of adult incarceration. Despite its limitations, the technique of propensity score matching could profitably be applied to a number of additional research problems related to justice system involvement. A daunting challenge for any study of incapacitation is to estimate what would have happened had the incarcerated individual been free. In other words, on average, how many crimes the person would have committed if free. This study employs an approach that entails matching incarcerated individuals with non-incarcerated individuals on the basis of a propensity score created using information temporally prior to the treated individual’s first incarceration spell. Data were used from the first six waves of the National Longitudinal Survey of Youth 1997. This is a nationally representative sample of 8,984 youths born during the years 1980 through 1984 and living in the United States during the initial interview year in 1997. Tables, figures, appendix, and references