text: methods for calculating incidence are complicated and imperfect. It should be acknowledged in 
  advance that this paper does not fully resolve these issues. It is merely intended as a first step, 
  to obtain workable estimates upon which to base policy until more sophisticated methods are 
  developed. That said, every effort is made in this analysis to sense-check the results against 
  other available datasets. The datasets used and the structure of the paper is as follows. 
  
  i)**Drug Interventions Programme (DIP) data.**In part one, we produce general 
  
  descriptive statistics from these data, which capture individuals who test positive for 
  opiates/crack-cocaine following arrest or charge. Due to the limitations in coverage of 
  these data over time, we draw only broad conclusions, some of which act as a sense- 
  check for the main results from part two. 
  
  ii)**Data on presentations to treatment from the National Drug Treatment Monitoring**
  **System (NDTMS).**In part two, we use two models based on previous research papers 
  to calculate OCU incidence at the national level between 2005 and 2013. Most of the 
  main conclusions come from this section. 