In a recent paper published in this journal, Gottfredson and Hirschi (1986)' argue that the concepts of criminal careers, career criminals, selective incapacitation, prevalence, and incidence, and longitudinal studies all have little value for criminologv. In our view their paper misrepresents these concepts and our research on these topics. We are pleased to have the opportunity in this paper to develop these concepts more clearly and to show their relevance for criminology.

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Most knowledge about crime and criminals derives from cross-sectional analyses that link crime rates in a community with a community's attributes. The criminal-career approach focuses on individual offenders and considers their crime-committing patterns as a longitudinal stochastic process. This approach, which invokes parameters characterizing participation rate, initiation rate, termination rate and the associated career length, and individual offending frequency, offers some important new insights. For example, annual offending frequency appears to be reasonably constant with age for those offenders who stay criminally active, termination rates are relatively low for active offenders in their 30s, and offending frequencies seem to be relatively insensitive to demographic attributes for active offenders. All these observations are opposite to those that would be derived from cross-sectional analysis.

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