Bulletin no. 05: Estimating the number of heroin users in Australia

Rationale

Estimating the prevalence of drug use is one of the key focal areas of alcohol and drug epidemiology. Estimation of the extent of alcohol and drug use in the Australian community has primarily been undertaken using surveys of the general population. Nevertheless, it is widely understood that prevalence estimates derived from general population surveys underestimate the true extent of drug use in the community for drugs of low use prevalence (e.g. heroin) because of issues around sampling (e.g. response rates and the extent to which crucial samples such as the homeless are missed in household surveys) and the truthfulness of responses to questions concerning illegal or hidden behaviours. In response, epidemiologists have applied specialised statistical techniques to the analysis of data sources on the extent of drug-related harm (e.g. Opioid overdose deaths) to produce estimates of the extent of problematic drug use in the Australian community.

Prevalence estimation using secondary data sources has generally been undertaken only in relation to heroin use in Australia. This work has used a variety of techniques (e.g. capture-recapture, back-projection, multiplier) in accordance with a general consensus that has emerged around the application of such techniques to the estimation of problematic drug use. In applying these methods Australian work has developed multiple estimates using available statistical estimation tools with convergence among estimates used as the source of the most parsimonious estimate (e.g. the median of the estimates derived). While this approach is appealing, the resultant ‘best’ estimates are derived primarily from the application of simple mortality multipliers (e.g. 1% annual mortality rate for heroin users) to the number of opioid overdose deaths occurring in specific Australian jurisdictions (generally NSW). The problem of this multiplier approach is highlighted by the effect of the heroin shortage in Australia.

The aim of this component of the DPMP was to develop plausible estimates of the prevalence of heroin use in Melbourne with a view to informing various elements of DPMP projects. The work was also designed to provide a method for estimating the extent of injecting drug use more widely (specifically through application to amphetamines). It was funded by a Travelling Scholarship from the Victorian Premier’s Drug Prevention Council awarded to Paul Dietze.