Final answer:
Cluster sampling is a probability sampling method used when it is difficult to collect data from the entire population, targeting groups or 'clusters' for easier data collection.
Step-by-step explanation:
Cluster sampling is a probability sampling method. In cluster sampling, researchers divide the population into separate groups, known as clusters. Clusters are often selected based on demographic or regional lines, and then a random sample of clusters is chosen. Within each of the chosen clusters, either all individuals are included or a random sample of individuals is selected to be part of the survey. This process ensures that each individual has a chance of being selected, which is a key characteristic of probability sampling methods. Cluster sampling is particularly useful when it is difficult or expensive to collect data from the entire population. It provides a cost-effective way to sample populations that are spread out geographically or are otherwise difficult to access.