This document discusses census and sampling methods for collecting population data. A census collects data from all members of the population, while sampling collects data from only a subset. Sampling is faster, cheaper, and more adaptable than a census but less accurate. Probability sampling methods like simple random and stratified random sampling allow accurate error estimation, while non-probability methods do not. Both methods have advantages and disadvantages related to accuracy, costs, and error estimation. The document also defines sampling error and non-sampling error and their sources.