text: The coverage of the DIP data 
  
  The DIP data will not capture all OCUs for several reasons. 
  
  i) 
  
  It is predicated on arrest or charge, so OCUs who do not commit crime will not be 
  captured in the data. 
  
  ii) Data are not available for all months in each year – data for 2013 are only available for 
  
  the first 11 months of that year. 
  
  iii) Its geographical coverage is not 100 per cent and varies across the period in question. 
  iv) The data do not cover all ages. DIP tests are given to those aged 18 and over only 
  
  (and we excluded those over 60 for various reasons). 
  
  iv) Other factors, like data-entry error. In particular, the exclusion of those without an entry 
  
  on the Police National Computer (PNC) will affect DIP coverage. 
  
  This section tries to assess the seriousness of these issues when interpreting the DIP data and 
  drawing conclusions. Regarding the first and fourth points, it is clear that the DIP data presented 
  in this report are only informative about a subset of OCUs, those who commit crime and are 
  aged between 18 and 59, and all inferences from the data must reflect this. Point ii) has been 
  dealt with throughout the paper by adjusting 2013 figures in a linear fashion to account for the 
  missing month. This also needs to be borne in mind when interpreting the findings. 