Public health surveillance is important for the health of any nation. In order to decide how to allocate resources, it is vital to know who is being affected, where those people live, and the timeliness of the issue. There are many sources of public health data that can be used to achieve these goals including vital records, mandatory reporting, registries, and health surveys. Surveys are used to gather information that is not standardly or systematically collected. Since we often cannot gather data on the entire population of interest, we need to select a subgroup to sample from, and different methods for sampling were outlined in this lesson.