Sampling

Sampling is the process of selecting units for study that will be representative of a population so that one can make generalizations about that population. A key distinction in sampling is between the theoretical population and the accessible population. Often the theoretical population is not known or could be known only with great cost and difficulty, but the accessible population is one that is more delimited and that the evaluator can with confidence identify and thus select from. Samples can be selected randomly, purposively, or accidentally. Random, or probability, sampling involves a prespecified set of procedures for selection and may be simple, stratified, clustered, or combined into a multistage sampling plan. Purposive sampling begins with an interest in a particular group—the evaluator chooses units based ...