text: 4 The average is useful, but hides the fact that offending within the opiate/crack population is highly skewed with a few 
  
  individuals responsible for the majority of crime and many individuals manage to use heroin and crack without resorting to 
  acquisitive crime at all (Morgan, 2014). 
  
  5 Though regular national-level estimates have not been attempted, studies have estimated incidence at various times and at 
  various different levels of geography, see for example: De Angelis et al., 2004, Millar et al., 2001 and Hickman et al., 2001. 
  
  New opiate and crack-cocaine users: characteristics and trends  4 