Modelling Illegal Drug Participation in Australia

AuthorsSarah Brown, Mark Harris, Preety Srivastava
PublishedJuly 2013
PublisherCurtin University
Number of Pages46


We contribute to the small, but important, literature exploring the incidence and implications of mis-reporting in survey data. Specifically, when modelling “social bads”, such as illegal drug consumption, researchers are often faced with exceptionally low reported participation rates. We propose a modelling framework where firstly an individual decides whether to participate or not and, secondly for participants there is a subsequent decision to mis-report or not. We explore mis-reporting in the context of the consumption of a system of drugs and specify a multivariate inflated probit model. Compared to observed participation rates of 12, 3 and 1.3%(marijuana, speed and cocaine, respectively) true participation rates are estimated to be some 5 percentage points higher for marijuana, and nearly double for cocaine. There was an estimated 36% (18%) percent chance that a cocaine (marijuana) user would mis-report their participation. Less evidence of mis-reporting was found for speed users.