PROBABILISTIC MODELS OF YOUTHFUL CRIMINAL CAREERS

This paper focuses on the characterization of the criminal careers of youthful offenders. It was found that these criminal careers could be modeled with parameters rejecting constant individual rates of offending and constant probability of career termination; population heterogeneity could be adequately represented by two distinct groups—designated here as "frequents" and occasionals." These parameters were estimated for the multiple offenders in a London cohort studied from their first convictions until age 25. In that cohort, the frequents were estimated to have an annual conviction rate of 1.14 convictions per year (constant with age) and a probability of career termination of .10 following each conviction; the occasionals had an annual conviction rate of .41 and termination probability of .33 following each conviction; the frequents were estimated to comprise 43% of the population, and the occasionals the others 57%. While this parsimonious model structure was adequate for the London cohort, it must still be tested with other offender populations.