A Capture–Recapture Model to Estimate the Size of Criminal Populations and the Risks of Detection in a Marijuana Cultivation Industry

Abstract

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.