text: before 1960 was removed and because DIP tests are only administered to those aged 18 and 
  over, so only using data to 2013 means it would not be possible for anyone to be born in 1996 
  or afterwards to be included. Even so, it is clear from the year-of-birth distribution (Figure 2) that 
  positive opiate tests drop off sharply for those born after 1982. This is in line with other evidence 
  suggesting that the number of new users of opiates decreased sharply in the 2000s. This needs 
  to be considered when interpreting the analysis that follows. When DIP and the NDTMS 
  treatment system began in the mid-2000s, there already existed a cohort of around 320,000 
  OCUs, according to available estimates by Hay et al., (2013). And most of these individuals 
  began using opiates/crack during the epidemic years of the 1980s and 1990s. In terms of data 
  capture this means it is hard to separate the gradual inclusion of more and more individuals 
  from this original cohort from genuinely new users of these drugs. 