The amount of delinquent activity

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The number of recorded criminal incidents in a delinquent career is an indicator of the overall extent of the offender's delinquent activity. Most offenders in both birth cohorts were involved in only one recorded incident during the 10 year observation period. A minority had very active careers. On average, offenders born in 1987 were implicated in 2.4 recorded incidents between their 8^th and 18^th birthdays. These included an average of 2.1 incidents involving at least one substantive offence and 0.3 incidents involving only alleged offences against the administration of justice¹. Average career activity was somewhat less for the 1990 cohort: an overall average of 1.7 incidents between the 5^th and 15^th birthdays, of which 1.6 were substantive incidents. This reflects both the less intense recorded criminal activity characteristic of younger children, and the virtual absence of offences against the administration of justice before the age of criminal responsibility is reached at the 12^th birthday: since children under 12 cannot be charged with, or found guilty of, criminal offences, they are not at risk of committing the common administrative offences of violation of bail or probation conditions, or failure to appear for court.

One of the most striking findings of research on delinquent and criminal careers is the uneven distribution of criminal activity among offenders. This was first documented in the classic study by Wolfgang et al. (1972) of boys in Philadelphia, which found that a small number of very active offenders were responsible for the majority of recorded crime committed by members of the birth cohort: 52% of the recorded crimes were committed by the 18% of offenders who committed five or more recorded offences, and were termed "chronic" offenders in the study. Those chronic offenders averaged 8.5 recorded offences between their 7^th and 18^th birthdays. On the other hand, almost half the offenders in the birth cohort (46%) committed only one recorded offence during the period of observation. This result has been replicated in many different studies. For example, in their study of the "court careers"² from the 12^th to the 22^nd birthday of Canadians born in 1979/80, Carrington et al. (2005) found that 16% of the offenders who had five or more incidents in their court careers were responsible for 58% of all incidents, and that 55% of the offenders had only one incident in their court career.

Figure 31 and Table 5 show the breakdown of offenders and their activity in the 1990 and 1987 birth cohorts, using the same classification scheme as Wolfgang et al. The uneven distribution is evident in both cohorts. Chronic offenders make up only 10% of offenders born in 1987, but they account for 46% of recorded incidents involving members of that cohort; they averaged 10.8 incidents per offender. On the other hand, 63% of offenders born in 1987 had only one recorded incident in their delinquent careers.³

The three categories of offenders in Wolfgang's typology give only a crude picture of the inequality of recorded delinquent activity. The Gini coefficient is a more precise indicator of inequality which is based on the entire distribution of criminal activity. This index is commonly used to measure inequality of the distribution of wealth or income in a population, and ranges from 0 (for a perfectly equal distribution) to 1 (for a perfectly unequal distribution). The values of the Gini coefficient for the number of recorded incidents in the careers of members of the 1987 and 1990 cohorts are 0.49 and 0.37 respectively (Table 5), confirming the greater inequality of activity in the 1987 cohort.⁴

The inequality of criminal activity decreases slightly if attention is restricted to substantive incidents – that is, if incidents which involve only administrative offences are excluded. The proportions of chronic offenders born in 1987 and 1990 decrease from 10% and 5% to 8% and 4% respectively, and the values of the Gini coefficient and standard deviation are also slightly lower (Table 5).

Table 6 shows the total recorded frequency of offending broken down by sex. Male offenders were more active than females, having an average of 2.7 recorded incidents in their careers, versus 1.8 for girls, in the 1987 cohort. Similar differences exist in the 1990 cohort. The more intense delinquent activity of boys is expressed more in a higher proportion (13%) of male than female (5%) chronic offenders, in the 1987 birth cohort, than in the average level of activity of those chronic offenders, which is not strongly differentiated by sex –11.0 incidents for male chronic offenders and 9.4 for females. Chronic offenders were responsible for half (51%) of all recorded incidents involving boys born in 1987, compared to only 27% for girls. The comparative results are similar in the 1990 cohort. The greater differentiation, or inequality, of activity among boys is also indicated by the Gini coefficients: for boys in the 1987 cohort, it is 0.52, for girls it is 0.38. The results for boys can be compared with those reported for boys in Philadelphia, some 30 or 40 years earlier, by Wolfgang et al. (1972). Wolfgang et al. found that the 18% of chronic (male) offenders averaged 8.5 recorded offences and were responsible for 52% of the cohort's recorded crime; the present study found that the 13% of chronic male offenders born in 1987 averaged 11 recorded offences, and were responsible for 51% of the cohort's recorded crimes. One-time offenders made up 46% of the offenders in the Wolfgang study, and 59% of male offenders in the present study.

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Notes

1. "Substantive offences" refers to all offences except administrative offences (offences against the administration of justice). The most common administrative offences are violations of bail or probation conditions, or failure to appear for court. Other, much less common administrative offences include prison breach, escaping from custody, and other very infrequent offences. See Table A.1 in the Appendix for a detailed breakdown of offences allegedly committed by members of the study population.
2. I.e. the incidents which resulted in charges which were heard in youth court or adult criminal court.
3. There are fewer chronic offenders in the 1990 birth cohort, because it is observed in this study over a period of life during which recorded offending activity is less intense. Only 5% of offenders born in 1990 fall into the "chronic offender" category, but their average level of activity (9.3 incidents per offender) is almost as high as that of chronic offenders born in 1987. Chronic offenders account for 27% of incidents involving members of the 1990 birth cohort. Seventy-four percent of offenders born in 1990 had only one recorded incident between their 5^th and 15^th birthdays. Like the comparison made above of the mean number of incidents in the career, the distribution of members of the 1990 birth cohort into Wolfgang's three categories reflects both the less intense recorded substantive criminal activity of these younger children , and their not being at risk of committing the most common types of offences against the administration of justice until they reached the 12^th birthday.
4. Calculation of the Gini coefficient requires unweighted data, so these values are based on raw frequencies rather than the weighted population data used elsewhere in this report. Another index of inequality is the standard deviation, which can be calculated using weighted data, but is less straightforward to interpret because it does not have a fixed maximum value. Values of the standard deviation of the distributions of recorded activity for the 1987 and 1990 cohorts are 4.5 and 2.5 respectively (Table 5).