When each member of the population has a known probability, then it is called probability sampling. The examples of probability sampling are simple random sampling, stratified random sampling, cluster sampling. A cluster is a collection of units in nature. If the probability of selection of a unit from a population is considered equal, the probability is called simple random sampling. In stratified random sampling the population is divided into two or more homogeneous groups and sample is chosen from these groups. The sampling in which personal judgment determines that which unit of the population are selected is called non probability sampling. Moreover, quota sampling, purposive sampling are the examples of non probability sampling.
