Stratified Sampling

Stratified sampling is a method of random sampling. In stratified sampling, the population is first divided into homogeneous groups, also called strata. Then, elements from each stratum are selected at random according to one of the two ways: (i) the number of elements drawn from each stratum depends on the stratum’s size in relation to the entire population (“proportionate” sampling), (ii) the number of elements sampled from each stratum is not proportionate to the size of the stratum (“disproportionate” sampling); in this case, an equal number of elements is typically drawn from each stratum and the results are weighted according to the stratum’s size in relation to the entire population.