Unequal probability sampling is a method used in survey design to select samples with varying chances of being chosen. Researchers have developed many algorithms for this type of sampling, with over 50 proposed so far. Multistage sampling is one application of this method, where primary units are selected with different probabilities. For example, self-weighted two-stage sampling selects primary units based on the number of secondary units within them. This approach helps in creating representative samples for surveys without replacement.