text: cocaine users. In addition, the sharp decline in total DIP tests in 2013 may be due in part to the 
  fact that DIP ceased to be a nationally funded programme in April 2013. 
  
  These data do show, however, that from 2006 onwards, between a third and half of all 
  acquisitive crime arrests involved a drug test and between 15 per cent and 35 per cent of those 
  tests (depending on the year) resulted in a positive result for opiates-only or for both opiates and 
  cocaine (hereafter labelled `positive-for-both’). 
  
  The reason for highlighting only the opiates-only and the `positive-for-both’ test results is that 
  the primary group of interest in this report are opiate and crack-cocaine users. To capture this 
  group, cocaine-only tests must be excluded because DIP tests cannot distinguish between 
  powder- and crack-cocaine, so a cocaine-only positive test could indicate either. Previous 
  evidence has demonstrated that while there is much overlap between heroin and crack-cocaine 
  cohorts (i.e. many of those who use heroin also use crack-cocaine), powder-cocaine users have 
  a quite different profile and are far less likely to be involved with acquisitive crime. Excluding the 
  cocaine-only tests means we can be guaranteed not to capture any powder-cocaine users (who 
  are not also using opiates or crack), but it also means we may miss some crack-cocaine-only 
  users, hence the figures may under-estimate the true population of OCUs slightly. 