A vast body of research shows important differences among segments of the population on virtually all aspects of health and health care, including patterns of disease and disability, use of services, and quality and outcomes of care. Documenting such differences is an essential starting point for a wide array of policies and interventions to improve peoples’ health. Biological, cultural, historical, and socioeconomic differences among different segments of the population may create distinctive patterns of health care needs and differences in the use of and responses to medical services. Understanding the patterns and differences is impossible unless researchers can separate and compare data from various segments of the population. That is difficult when those population segments are small or difficult to identify. This is a particular concern when the small population in question has special vulnerabilities or may be subject to inequitable treatment. To date, the federal government’s very substantial data collection efforts have not generated adequate data about some subpopulations because of their small size or their distribution (either great concentration or lack of concentration) or because of insufficiently standardized ways of identifying the population in a survey context.
The small size of some populations means they may not be included in numbers sufficient for separate analyses in federal surveys. Also, information identifying some small populations may not be routinely included in the medical records and insurance claims that are another source of data. To illustrate the different research and methodological challenges facing research on small populations, this report focuses on four case examples—Asian-American subpopulations; lesbian, gay, bisexual, and transgender (LGBT) populations; adolescents with autism spectrum disorders (ASDs); and residents of rural areas. This report is about why research is needed about small populations such as those that we have chosen and about the challenges that small populations pose for research; we make no attempt here to report comprehensively on the health and health care needs of the four populations. We also recognize that many other relatively small populations may have special health care needs or pose particular challenges to the health care system. Our cases are illustrative of a more general set of issues.
Advocacy organizations, as well as some researchers and policymakers, have pushed for the collection of more data about various small populations, including the examples we focus on in this report. With the growing use of electronic health data in the provision of medical care, the possibility that such data might be used for research that complements or supplements existing federal data collection activities merits consideration. That is the topic of Part II of this report. For purposes of this report, we define “research” broadly as addressing issues traditionally addressed through clinical, pharmaceutical, health services, public health, public policy, and evaluation research.