Survey sampling is a field of statistics that describes the process of selecting a sample of elements from a target population to conduct a survey. The term sampling may refer to many different types of techniques or observations. In other words, survey sampling is done by taking a sample out of the total population being sampled. The name sampling survey itself means that the survey is sample of the whole.
Survey samples can be basically divided into two types:
are those which have some kind of probability involved in the sampling. These can provide design based inference about the target population. The inferences are based on the known probabilities of inclusion that were specified in the study protocol.
are those which are not based on a probability sampling scheme. Non-Probability samples are very tough to act upon. They often fail to represent the people in the target population.
There are numerous ways of getting a sample from a whole list of a population or a map of the area to be sampled, but the most commonly used are
Random Sampling: This is the purest form of sampling under the probability approach. It provides an equal chance of being picked for each member of the target population.