Cohort members’ complete recorded offending history (up to 31st March 2009) was extracted from the Police National Computer (PNC). Age at drug-use initiation was obtained for the subset also recorded in the English National Drug Treatment Monitoring System (NDTMS) over the same period. The analysis cohort was identified from those who received a saliva drug test for opiate and cocaine metabolites following arrest, as recorded by the Drug Test Record (DTR), over the period 1st April 2005 to 31st March 2009. Information about the age of first opiate use is used to consider whether the contrast between opiate positives and test-negatives is similar both before, and after, the initiation of opiate use. This comparison is performed for all offences committed and for three offence categories (serious acquisitive, non-serious acquisitive, violent) whilst controlling for age and birth cohort, and separately by gender. We therefore focus on opiate use, by comparing the historical offending trajectory of offenders who test positive for opiate use (opiate positives) with a control group who test negative for both opiate and cocaine use (test-negatives). Prior analysis on this cohort considered offending rates in the two years prior to drug-test and found that testing positive for opiates was a greater predictor of excess offending than testing positive for cocaine. This paper reports a retrospective cohort analysis to compare the historical offending trajectory of offenders according to drug test result. Similarly, gender is known to be a strong influence on offending trajectories and whilst some studies have shown the pre/post contrast is greater for females ( Degenhardt et al., 2013), the lack of adequate comparator groups limits the inferences which can be drawn. To disentangle the age effects from those of drug-use initiation, it is crucial to control for age, using an appropriate control group. For example, a large proportion (45%) of users in treatment services in the North West of England report age at first use of heroin between 15 and 19 years of age ( Advisory Council on the Misuse of Drugs, 2006). In general population samples, offending rates tend to peak during late adolescence ( Sweeten et al., 2013) which coincides with the age of drug-use initiation. This pre/post design fails to separate the effects of initiation from the effects of other factors which might also be related to offending, in particular, age, which correlates strongly with offending. Most studies which make this comparison find that offending rates are substantially higher after drug-use initiation ( Hayhurst et al., 2017). A typical example is the study by Anglin and Speckart (1988), which examined the criminal records and clinical data of male methadone patients.
Our recent review of the evidence base on pathways through opiate use and offending ( Hayhurst et al., 2017) highlighted that research has focused on comparing offending that occurs prior to the initiation of drug use with offending that occurs thereafter.
Whilst cross-sectional studies can provide information on the extent of the drug-crime association and its strength for different subgroups and offences, the aetiological debate requires longitudinal data to establish the timing of events and to gain knowledge on how the differences between users and non-users evolves over a person’s lifetime.Ĭurrent evidence about the development of drug use and offending is constrained by design flaws in published studies, particularly the absence of suitable control groups. Our previous work has highlighted the need for longitudinal studies with a non-drug user comparison group to examine the natural history of drug use and offending ( Hayhurst et al., 2017). The underlying causal mechanism(s) is likely to be more complex than these explanations suggest ( Bennett and Holloway, 2009, Seddon, 2000). Confounding – crime and drug use share a common (set of) cause(s): there is no direct causal relationship rather drug use and crime co-occur because of a common cause or set of causes ( Seddon, 2006, Seddon, 2000).