National probability samples in studies of low-prevalence diseases. Part I: Perspectives and lessons from the HIV cost and services utilization study

Objective. To examine the trade-offs inherent in selecting a sample design for a national study of care for an uncommon disease, and the adaptations, opportunities and costs associated with the choice of national probability sampling in a study of HIV/AIDS. Setting. A consortium of public and private funders, research organizations , community advocates, and local providers assembled to design and execute the study. Design. Data collected by providers or collected for administrative purpose s are limited by selectivity and concerns about validity In studies based o n convenience sampling, generalizability is uncertain. Multistage probabili ty sampling through households may not produce sufficient cases of diseases that are not highly prevalent. In such cases, an attractive alternative de sign is multistage probability sampling through sites of care, in which all persons in the reference population have some chance of random selection t hrough their medical providers, and in which included subjects are selected with known probability. Data Collection and Principal Findings. Multistage national probability sam pling through providers supplies uniquely valuable information, but will no t represent populations not receiving medical care and may not provide suff icient cases in subpopulations of interest. Factors contributing to the sub stantial cost of such a design include the need to develop a sampling frame , the problems associated with recruitment of providers and subjects throug h medical providers, the need for buy-in from persons affected by the disea se and their medical practitioners, as well as the need for a high particip ation rate. Broad representation from the national community of scholars wi th relevant expertise is desirable. Special problems are associated with or ganization of the research effort, with instrument development, and with da ta analysis and dissemination in such a consortium. Conclusions. Multistage probability sampling through providers can provide unbiased, nationally representative data on persons receiving regular medic al care for uncommon diseases and can improve our ability to accurately stu dy care and its outcomes for diseases such as HIV/AIDS. However, substantia l costs and special circumstances are associated with the implementation of such efforts.