Stratified Random Sampling

Stratified random sampling is a method for sampling from a population whereby the population is divided into subgroups and units are randomly selected from the subgroups. Stratification of target populations is extremely common in survey sampling. Stratified sampling techniques are often used when designing business, government, and social science surveys; therefore, it is important for researchers to understand how to design and analyze stratified samples. To obtain a stratified sample, members of a population are first divided into nonoverlapping subgroups of units called strata. The strata must be mutually exclusive and exhaustive, and there is an assumption of homogeneity within the strata. Following stratification, a sample is selected from each stratum, often through simple random sampling.