INDIRECT ESTIMATES OF HIDDEN POPULATIONS - CAPTURE-RECAPTURE METHODS TO ESTIMATE THE NUMBERS OF HEROIN USERS IN THE AUSTRALIAN-CAPITAL-TERRITORY

This paper describes a method of estimating the size of a population b ased on matching the individuals from the population appearing in two or more nonrandom samples. The method has been developed by population biologists and demographers who have shown that the simple estimates based on only two samples are very sensitive to the assumption that th e two samples are independent. This assumption is rarely met with huma n populations. However, estimates based on three or more samples can b e derived by fitting a loglinear model to a 2k contingency table. The method is applied to a data set of heroin users seeking treatment or c ounselling or arrested on drug charges in 1988 or 1989 in a small Aust ralian city. The method produced a stable estimate of 1250 heroin user s. This includes only users who are vulnerable to arrest and/or intere sted in seeking treatment. Although estimates produced by this method should be validated with other techniques it provides a simple, quick method to estimate the numbers of people in other hidden populations w hich are difficult to access.