3.1.10 Restricted Random Sampling
Stratified random sampling or simply stratified sampling is one of the random methods which, by using the available information concerning the population, attempts to design a more efficient sample than obtained by the simple random procedure.
While applying stratified random sampling technique, the procedure followed is given below.
1. The universe to be sampled is subdivided (or stratified) into groups which are mutually exclusive and include all items in the universe.
2. A simple random sample is then chosen independently from each group.
This sampling procedure differs from simple random sampling, where in the latter the sample items are chosen at random from the entire universe. In stratified random sampling the sampling is designed so that a designated number of items is chosen from each stratum. In simple random sampling the distribution of the sample among strata is left entirely to chance.