We use registers to track people who report certain conditions.
One goal may be to identify subjects for research.
Another might be to estimate the incidence, prevalence and outcome of rarer conditions.
These types of data collections are greatly influenced by case definitions—the standards physicians use in reporting cases to a registry. The laws governing medical practice require physicians and other care providers to report these cases to state and local government authorities who in turn send records based on these reports to the federal public health authorities.
As their understanding of a condition—such as AIDS—increases the case criteria may change thereby making it difficult to report change from one time to the next. Registers have been established to record and trace the incidence and outcomes of cases of particular diseases. For example, the National Cancer Institute at NIH has worked to establish SEER the Surveillance Epidemiology and End Results program. This program has established registries of cancer cases which serve as the basis for estimates of the incidence of cancers and their outcomes.
CDC has established a National Program of Cancer Registries [NPCR] which extends the collection of registry data to all 50 states and the District of Columbia.