Analytical Considerations in the Use of Capture-Recapture to Estimate Prevalence: Case Studies of the Estimation of Opiate Use in the Metropolitan Area of Barcelona, Spain

Abstract

Capture-recapture, an indirect method widely used to estimate undetected populations, has been criticized because it causes problems due to a lack of compliance with several important assumptions and model selection strategies. This paper expands on the problems encountered when applying this methodology to drug abuse estimations, specifically the prevalence of opiate use in the metropolitan area of Barcelona, Spain, in 1993. Three samples of opiate users (from hospital emergency rooms, treatment centers, and prisons) were available in the area studied; an additional sample (mortality data) was analyzed for the city of Barcelona. Log-linear models that provided a good fit were considered, to which further model selection strategies were applied. A total of 3,207 unique individuals aged 15-44 years were identified in the three samples from the greater Barcelona area; the mortality sample from the city of Barcelona contained an additional 83 individuals. Heterogeneity was observed in different age, sex, and residence area subgroups. Population estimates differed widely according to the log-linear model chosen. Minimum Akaike's information criterion model and saturated model estimates were used to produce population prevalence rates. The main problems the authors encountered in this study were related to population definition, source heterogeneity, and assessment of an adequate model, a problem associated with sample size.

Estimating the size of the population of persons who inject drugs in the island of Montréal, Canada, using a six-source capture–recapture model

“…As other studies have demonstrated (Hser, 1993;Domingo-Salvany et al, 1998;Platt et al, 2004;Hickman et al, 2004;Böhning et al, 2004;Chiang et al, 2007;Khazaei et al, 2012;Pérez et al, 2013;Uuskula et al, 2013), the CRC approach, despite its limitations, is useful to estimate the size of PWID populations. This approach can be of particular interest when conducted at regular intervals thus allowing for close monitoring of the injection phenomenon and optimal provision of services to this high-risk population.…”

“…Using a short reference period has been suggested as a way to minimize the impact of this bias (Domingo-Salvany et al, 1998). Population movements should have been limited during the chosen one year period.…”

“…CRC was initially developed in animal ecology and introduced in epidemiology in the 1970s by Wittes (Wittes et al, 1974;Wittes and Sidel, 1968). It has been widely used to estimate the prevalence of problematic drug use around the world (Hser, 1993;Domingo-Salvany et al, 1998;Platt et al, 2004;Hickman et al, 2004;Böhning et al, 2004;Chiang et al, 2007;Khazaei et al, 2012;Pérez et al, 2013;Uuskula et al, 2013).…”

Estimating the number of drug users in Bangkok 2001: A capture–recapture approach using repeated entries in one list

“…From 1981 to 1990 19 papers were found, whereas from 1991 to 2002, 210 publications were detected. Some recent applications of capture-recapture techniques to illicit drug use were the estimation of injecting drug users in Edinburgh, Scotland, 1992Scotland, -1994, the size of opiate use in Barcelona, Spain 1993 [5], the estimation of opiate users in Amsterdam, Netherlands, 1997 [6], the amount of drug misuse in urban and non-urban settings in the north-east of Scotland [7], and the estimation of prevalence of opiate use in Dublin, Ireland [8]. For Thailand, there have been only a few studies of this kind including a study on HIV-infected injection drug users in Bangkok 1991 [9].…”

“…In the field of drug use, these sources are often a hospital-like institution and the police (if there are two sources [8,9]) or treatment centers, surveys, family doctors etc. (if there are several sources [4][5][6][7]). If there are only two lists, an estimate for the population size can be constructed by multiplying the frequencies of persons identified by each list and dividing the result by the frequency of persons found on both lists, the Lincoln-Petersen estimate [10].…”