New opiate and crack-cocaine users: characteristics and trends 11 
 
Figure 3: Distribution of tester’s age at positive test for all opiate-only/positive-for-both tests. 
 
Note: as a guide to the OCU population, this chart is left-truncated as DIP tests are not given to under-18s.  
The above statistics include tests in which no Police National Computer (PNC) number was 
recorded for an individual. This number is needed to identify an individual and hence to check 
whether future tests are further tests by that individual or represent a new individual testing 
positive. Excluding tests in which no PNC number was recorded makes little difference to the 
descriptive statistics, see Table 3 below.