Probability sampling

A sampling procedure in which each element of the population has a known non-zero chance of being selected for the sample. The chances of each member of the population being included in the sample may not be equal, but every one has a known probability of inclusion. That probability is determined by the specific mechanical procedure that is used to select sample elements. In this type of sampling, it is required that not only precise definition of the target population, but general specification of the sampling frame have to be clearly stated because sample elements are selected by chance, it is possible to determine the precision of the sample estimates of the characteristics of interest.