New opiate and crack-cocaine users: characteristics and trends 18 
 
Table 7: Number of unique individuals testing positive for opiates-only or positive-for-both, 
by year of first positive test. 
  Number of unique individuals with positive opiate/opiate + cocaine tests per year  
First test year 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 Adjusted 2013 
2004 12,246 3,171 3,299 3,090 2,992 2,573 2,311 1,766 1,513 1,092 1,191 
2005   10,539 3,020 2,539 2,478 2,083 1,844 1,350 1,156 862 940 
2006     14,750 3,896 3,280 2,701 2,507 1,819 1,610 1,140 1,244 
2007       13,391 3,063 2,291 2,091 1,567 1,334 954 1,041 
2008         13,629 2,670 2,263 1,612 1,366 978 1,067 
2009           11,655 2,211 1,431 1,125 847 924 
2010             10,391 1,385 1,052 733 800 
2011               7,913 1,017 643 701 
2012                 6,022 823 898 
2013                   4,281 4,670 
Total  12,246 13,710 21,069 22,916 25,442 23,973 23,618 18,843 16,195 12,353 13,476 
 
These tables can be read both horizontally and vertically. Reading vertically (i.e. down the 
columns) it can be observed, for example, that of the 12,353 individuals with a positive test in 
2013, 4,281 (35%) had not had a previous positive test and over half had already tested positive 
at least once in 2010 or before. 
Reading horizontally – for example from left to right across the first row – it can be concluded 
that of the 12,246 individuals testing positive in 2004, 3,171 also had a positive test in 2005; 
3,299 of the original 12,246 also had a positive test in 2006 and so on. The table does not show 
whether those who had a subsequent test in 2005 were the same individuals as those who had 
a subsequent test in 2006. So reading the results of the two tables together, we can say that 
12,246 individuals had 17,174 positive tests in 2004, and of these, 3,171 also tested positive in 
2005, resulting in 5,604 positive tests because some tested positive more than once in that 
year. The last figure in each column gives the number of new users that year (10,539 in 2005, 
14,750 in 2006 and so on).   
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