Abstract
Information from experts, or "key informants," is often used when estimating the prevalence of a disease, the numbers in particular risk groups, or the frequency of particular risk behaviors. This study aimed to better understand and describe the usefulness of key informants in informing an area such as injection drug use, where the populations are often marginalized and difficult to identify and the illnesses (HIV and hepatitis C virus) associated with the risk behavior can lead to discrimination by the general community. Our study results highlight the limitations of relying upon key informant information alone to provide specific information or accurate data about ethnic Vietnamese injection drug users. While exercises such as the Delphi technique can be used to generate the broad views and opinions of experts around a particular issue, we argue that care must be taken when using such information as evidence on which to base the direction and design of social and public health policy and resources, particularly in relation to marginalized populations.