This document discusses sampling methods for collecting data. It outlines two main methods: census and sampling. The census method collects data from every unit in the population but is costly and time-consuming. The sampling method collects data from a subset of the population and inferences can be made about the whole population. There are random sampling methods like simple random sampling and stratified sampling that allow statistical analysis, as well as non-random methods like judgment sampling. Sampling provides benefits like lower cost and time compared to a census, but must be carefully designed to avoid bias.