Collecting data to evaluate the effect of health policies on vulnerable populations.

Public health policies often have disproportionate effects on the poor and other vulnerable groups. Standard survey techniques are often difficult to apply to these vulnerable populations, and many data bases systematically omit such individuals. The purpose of this paper is to review our experience in collecting primary survey data from public hospital, mentally ill, HIV-infected, and non-English-speaking patients. Important issues in conducting research on these populations include proper selection of subjects and comparison groups and difficulties involved in recruitment and enrollment of subjects. Maintaining longitudinal data on these populations is difficult and often requires tracking, secondary contacts, home visits and community outreach, and the use of organizations, institutions, and networks. Investigators must also pay careful attention to ethical issues involved in conducting research on vulnerable populations.