The Cambridge Study of Delinquent Development was a prospective longitudinal study of 411 males born in 1953. They were first contacted in 1961 to 1962 and at that time they were all living in a working class area of London in the United Kingdom. They were selected by collating all of the boys who were aged 8 or 9 and registered in six state primary schools in approximately a one mile radius around the research office. The boys were almost all white and their parents had been raised in the United Kingdom or Ireland. The sample was interviewed and tested in their school at ages 8, 10 and 14; then they were interviewed at the research office at ages 16, 18, 21 and 24; and finally they were interviewed in their homes at age 31-32. A number of searches were carried out in the Central Criminal Record Office in London to obtain the conviction records for the sample at each stage. Convictions were only recorded if they were for offences normally recorded by the Office. Therefore, all traffic offences, drunkenness and status offences (e.g. truancy) were excluded. Convictions were slightly less common than arrests as the vast amount of arrests received convictions. All analyses were conducted on the date of the offence and not on the date of the conviction.
The study was first directed by Professor Donald West who was then joined by David Farrington in 1969. The original aim of the study was to examine the development of delinquent and criminal behaviour in inner city youths. Between West and Farrington,
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they generated 4 books and over 60 papers describing results of the studies. For example, West and Farrington (1973; 1977) documented the existence of chronic offenders in the Cambridge Study. They noted that indicators of future chronic and persistent offending were detectable as early as age 8. They also found offending to be diverse in nature and he noted a number of social factors that influenced the continuity of offending over time: family structure, economic conditions, and marital status.
In another example, Barnett, Blumstein and Farrington (1987) examined the characterisation of criminal careers (from their first conviction to age 25) of youthful offenders and found that they could be represented by two distinct groups: „frequents‟ and „occasionals‟. The „frequents‟ had a career length of 8.8 years and the „occasionals‟ had a career length of 7.4 years. However, Barnett, Blumstein and Farrington (1989), using new data collected on the same sample from age 25 to 30 found that the criminal careers of the delinquents in the Cambridge Study were better represented by three groups: „frequents‟, „intermittents‟, and „occasionals‟.
Farrington (1989) also investigated the prevalence of offending. He found that vehicle theft and burglary were the most frequent crimes, whereas drug use and auto-theft were the least. Also, chronologically, petty theft was found to occur before fraud and assault, whereas vehicle theft, burglary and shoplifting tended to occur at the same age. The best childhood predictors of later criminal activity were troublesomeness, parents convicted of offences, impulsivity, low intelligence, low attainment, low income, poor housing and poor child rearing.
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Farrington (1991) also investigated specialisation in violent offenders and found the violent offenders did not appear specialise in violence. The violent offenders in the study committed on average 1.7 violent offences but an average of 5.3 nonviolent offences. Furthermore, he found that violent and non-violent persistent offenders were virtually identical in terms of childhood, adolescent and adult factors. Consequently, he concluded that violent offenders were essentially just frequent offenders, and that violent offences occurred at random in the criminal career.
Farrington (1992), using the same sample, found that the age of onset peaked at age 14 and again at age 17 in the sample. He found the average age of onset to be 17.5 years and that the average number of offences committed decreased with increasing age of onset; 8.1 offences were committed on average by those whose onset age was between 10 and 13, and 1.5 offences were committed on average by those whose onset age was between 21 and 32. Extremely early onset, age 10 to 11, was associated with especially frequent or persistent offenders who averaged 11.8 offences up to age 32. The average career length, that is the time interval between the first and last recorded conviction, was found to be 5.8 years and the average career length decreased as the age of onset increased Farrington (1992). For an onset age of 10 to 13, the average career length was 9.9 years and for an onset age of 21-32, the average career length was 0.7 years. However, extremely early onset offenders had a career length on average of 11.5 years. The most common offences were theft, burglary and vehicle theft.
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Farrington (1995) then conducted a follow up of these offenders at age 32. He found that males had become less deviant in absolute terms; however, those individuals who were more deviant at age 18 were also more deviant at age 32. Farrington suggested that settling down with a female partner and job stability as possible explanations for reduced offending. He also noted that the peak age of offending coincided with the peak age of affluence for many convicted males. These particular males tended to come from low income families at age 8 and tended to have low income themselves at age 32. However, they were relatively well-paid compared to non-delinquents at age 18, indicating that the link between income level and future offending is likely to be quite complex. The major risk factors for delinquency were found to be poverty, poor housing, living in public housing in the inner city, and socially disorganised communities.