text: There are several observations to be drawn from these tables. First, it is clear that a proportion 
  of opiate-using offenders offend over long periods of time. Nearly ten per cent (8.9%) of 
  individuals who tested positive for opiates at charge in 2004 also tested positive nearly a 
  decade later in 2013 (on arrest). And reading vertically, of the 12,253 individuals testing positive 
  in 2013, 1,092 (8.9%) had also tested positive almost a decade earlier. 
  
  Second, in relation to incidence, these numbers also allow for some back-of-the-envelope 
  modelling to address the extent to which the figure of 4,281 individuals, who are new positive 
  testers in 2013, is an under- or over-estimate of the number of new OCUs in total. Taking the 
  figures for 2008, when DIP was fully up and running, we know that around 25,000 unique 
  individuals had positive tests that year. This can be combined with available estimates of the 
  total OCU population (Hay et al., 2013) and the proportion who are likely to be offending 
  (Gossop et al., 2003; Morgan, 2014) to give an approximate arrest rate. i.e. if there were about 
  150,000 crime-involved OCUs through the period, this implies an arrest rate of about 17 per 
  New opiate and crack-cocaine users: characteristics and trends  18 