The hidden population: Some methodological issues about estimation of problematic drug use

AIM - This article analyses and discusses the estimation of serious or problematic drug use through an empirical example based on a local Swedish study in Gothenburg. METHODS AND DATA - This was a case-finding study with questionnaires directed at organisations which have contact with the target group. The material was supplemented with information from the two documentation systems DOK and ASI. A total of 2,148 reports were collected. Health care data of 1,096 individuals was also collected for analysis with the truncated Poisson method. Analyses with capture-recapture or truncated Poisson were conducted to calculate the size of the hidden population. RESULTS - The statistical analyses resulted in variable numbers for the hidden population, and the total prevalence of serious drug abuse in Gothenburg is estimated to be between 2,200 and 4,400 people. CONCLUSION - The study shows that estimation of the presence and prevalence of problematic drug abuse involves many methodological difficulties and challenges. The significant variation of the size of the hidden population presented in the study raises doubts about the reliability and validity of the different methods. The methods are clearly sensitive to the importance of fulfilling the different basic assumptions.