New opiate and crack-cocaine users: characteristics and trends 41 
 
 
Estimated proportion of OCU population covered by DIP. 
  2005 2006 2007 2008 2009 2010 2011 2012 201325 
Estimate of 
DIP’s 
coverage 
24.50% 94.4% 96.9% 97.4% 94.1% 97.5% 95.8% 98.4% 98.3% 
 
This lends a certain degree of confidence to the findings and suggests that the variation in 
geographical coverage from 2006 onwards will not bias the findings greatly. However, a few 
caveats need to be mentioned. 
i) The above percentages only excluded LAAs that did not record any cases for the entire 
year. It is possible some LAAs only recorded cases for certain months within a 
particular year. 
ii) Many of the findings from the report exclude cases in which no Police National 
Computer (PNC) number was recorded. Looking at the data it is clear that the 
proportion of cases without a PNC number varies across areas. So this will introduce 
some geographical bias. 
iii) Using the published OCU figures by LAA to estimate DIP’s geographical coverage 
involves the assumption that OCUs tend to get arrested in the same area in which they 
live and receive treatment. 
Supplementary DIP charts, showing age and year-of-birth distributions for the 296,008 PNC 
cases with positive opiate/opiate + cocaine tests. 
 
 
25  Note that although the geographical coverage in 2013 is high, the data only cover the first 11 months of that year.