A capture-recapture model to estimate the size of criminal populations and the risks of detection in a marijuana cultivation industry

Originally developed in biology, capture-recapture methodologies have increasingly been integrated into the study of human populations to provide estimates of the size of hidden populations. This paper explores the validity of one capture-recapture model-Zelterman's (1988) truncated Poisson estimator-used to estimate the size of the marijuana cultivation industry in Quebec, Canada. The capture-recapture analysis draws on arrest data to estimate the number of marijuana growers at risk of being arrested for a period of five years (1998-2002). Estimates are provided for growers involved in two different techniques: (1) soil-based growing, and (2) hydroponics. In addition, the study develops an original method to estimate the prevalence of cultivation sites at risk of detection. A first set of findings shows that the cultivation industry is substantial; the estimated prevalence of growers compares to estimates of marijuana dealers in the province. Capture-recapture estimates are also used to compare the risks of being arrested for different types of offenders. Results indicate that hydroponic growers-those involved in large scale and sophisticated sites-face lower enforcement-related risks than growers involved in smaller enterprises. The significance of these findings is discussed in the context of the widespread development, both in Europe and in North America, of a successful domestic production-driven, rather than importation-driven, marijuana trade.