Which sampling method does NOT ensure that each individual has an equal chance of being selected?

The correct answer is stratified sampling. In stratified sampling, the population is divided into distinct subgroups or strata based on specific characteristics, such as age, gender, or socioeconomic status. Researchers then take random samples from each of these strata. While this method ensures representation from each subgroup in the overall sample, it does not guarantee that each individual within the population has an equal chance of being selected. The selection depends on the stratification criteria, and the chances of selection for individuals within those strata may vary based on their representation.

In contrast, simple random sampling ensures that every individual has an equal probability of being chosen. Systematic sampling involves selecting individuals at regular intervals from a randomly ordered list, which also allows each individual to have an equal chance of selection. Cluster sampling divides the population into clusters and randomly selects entire clusters; while this approach introduces randomness in the choice of clusters, it does include every member of the selected clusters, thus giving individual members a chance based on cluster selection.