Methods used to collect data on health and health care can be characterized by the following features:

  • Sample versus census—Some data are collected for the entire population to which they apply; such data are sometimes referred to as census data. One example is the actual decennial census, which aims to obtain counts by geographic location and basic demographic characteristics for the entire resident population of the United States. However, the term census may be used to refer to any data collection aimed at collecting data for every unit in the population of interest (i.e., a subset of a larger population of emphasis). Conversely, many data cannot be collected for the entire population without excessive cost and/or a burden on respondents. Instead, the data are collected from a subset of the population, or a sample, that is selected (usually by randomization) in a way that makes it representative of the entire population; thus, estimates can be calculated from the sample that approximate those for the entire population.
  • Based on administrative records versus respondents—Some data are extracted from records that already exist because they are necessary for the administration of a program or intervention. Examples are government records (tax files, social security and Medicaid enrollment, school enrollment, accident reports), commercial records (health plan enrollment files, medical claims), and medical records (from physicians’ offices, hospitals, and other providers of health care). Other data are collected directly from respondents, for example, by interviewing individuals about their experiences. The line between the two may not be entirely distinct; for example, a physician might be asked to provide data derived from the medical records she uses in her practice; thus the data collection is respondent based, but the data are ultimately derived from administrative records. In the case of children, most respondent-based data are collected from proxy respondents (e.g., parents and caregivers). A third category to consider is that pertaining to clinical data, such as observational studies.
  • Population- versus service-based—Some data collection efforts focus on a general population defined only by broad demographic characteristics, such as all children under age 6 or all adolescent girls. (Note that population-based in this sense could encompass data collection using sampling, and thus is unrelated to census data collection from an entire population.) Other data collection

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