What does the longitudinal patterning of criminal activity over age look like? Such basic questions have been studied in the criminal career literature, sometimes resulting in different conclusions.

Prevalence provides a measure of how many individuals participate in a crime type in any period. The shape of the age-crime curve for prevalence is generally agreed upon by most criminologists as data typically provide similar conclusions regarding trends in shape (though self-report records sometimes show an earlier peak for some crime types and a later peak for others). Both official and self-report records suggest that the prevalence of offending increases to a peak in the teenage years, at about ages 15–19, and then declines in the 20s (Blumstein et al., 1986; Elliott et al., 1989; Farrington, 1986; Piquero et al., 2003; Wolfgang et al., 1987). Prevalence curves typically form the basis of many conclusions regarding the aggregate age/crime relationship.

On the other hand, estimates of individual offending frequency, though generally minimally studied, tend to vary considerably – often because the definition of individual offense frequency varies. Some researchers prefer to simply plot the number of offenses (frequency) engaged in by sample members over time or over a particular time period, while other researchers argue that individual offending frequency should be defined by the amount of crime engaged in over a particular time period among those offenders who are active (i.e., offending) during that time period.

The evidence on individual offending frequency is mixed.