New opiate and crack-cocaine users: characteristics and trends 22 
 
2. Estimating an incidence trend from 
treatment data 
This section uses treatment data from the National Database Treatment Monitoring System 
(NDTMS) to estimate the number of new OCUs annually. The NDTMS captures data on the 
numbers of people presenting to services with problem drug misuse and information about the 
drug treatment they receive. All drug treatment agencies in England provide a basic level of 
information to the NDTMS on their activities each month. The data for this report included all 
unique individuals presenting to treatment with opiates or crack-cocaine listed as their primary 
drug between 2005 and 2014. All individuals whose age of first use was listed as below ten or 
before 2005 were then excluded. Excluding individuals who started using opiates/crack before 
2005 resulted in a large number of records being left out, due to the fact that the majority of the 
treatment population, even in 2013/14, initiated in the 1980s and 1990s when heroin and crack 
use surged in the UK. However, this exclusion is necessary for the incidence methodology, as 
explained later in this section. The remaining dataset included 52,829 individuals, as shown in 
Table 10. 
Table 10: Descriptive statistics from the NDTMS data. 
Reason for exclusion  
Number of 
individuals 
excluded  
Total number 
of individuals 
analysed  
Initial sample prior to exclusion  0 243,588 
No age at first use recorded or age 
was below 10 or higher than age at 
first treatment 
443 243,145 
Year of first use before 2005  190,316 52,829 
Percentage of total sample 
initiating 2005–14 n/a 21.7% 
 
The majority of those presenting for treatment between 2005 and 2014 started using 
opiates/crack before 2005 (around four in five). Only 52,829 individuals said they had an 
opiate/crack initiation date between 2005 and 2014. This suggests an average of just under 
5,000 new starters per year during this period. But this would be an under-estimate of incidence 
because it is likely that some of those who began use between 2005 and 2014 would not yet 
have come to treatment during that period. 
To correct for this, we use two variants of a methodology employed by researchers in Millar et 
al. (2001) and Hickman et al. (2001). These papers discuss the methodology in detail.   
In brief, the method uses the lag-to-treatment distribution for the sample coupled with the 
number of new treatment presentations in a given year to estimate OCU incidence in that year. 
So, when presenting to treatment, all individuals are asked to provide the year in which they first 
began using their primary drug, which for this analysis was limited to opiates and/or crack-