a sample where every element of the target population has a known, non-zero probability of being selected

A sample selected in such a way that its characteristics can be generalized to the population from which it was drawn with a known degree of accuracy. The level of accuracy for proportions, means, and correlations is presented as a 95 percent confidence interval, which contains the true population value 95 percent of the time. See Locally representative sample.

A scientific sampling framework that relies on a representative selection from the population as a whole.

A research sample in which the elements are selected from a sampling frame with a known, non-zero probability of selection. Some common types of probability samples are: Simple random sample: Each element is selected at random from the population as a whole; Stratified sampling: The original sampling frame is divided into mutually exclusive sub-frames (strata) and separate and independent samples are selected from each strata. Multi-stage samples: Sampling elements are selected in stages. For example, the first stage might involve selecting block groups within counties. The second stage might then be a sampling of blocks. Different frames and different elements are usually used at each stage. The probabilities of selecting each element are known for each stage of selection. Cluster Sample: The sample elements are groups of units and not individual units. Each element is identified with only one cluster in the selection process.

A subset of the population chosen in such a way that every member of the population has a known (nonzero) chance of being selected into the sample.

A group of cases selected from a population by a random process. Every member of the population has a known, nonzero probability of being selected.

A sample drawn from a population using a random mechanism so that every element of the population has a known chance of ending up in the sample.