Stratified Sampling: If the population from which a sample is to be drawn does not constitute a homogenous group, then stratified sampling technique is applied so as to obtain a representative sample. In this techniques the population is stratified into a number of non overlapping subpopulations or strata and sample items are selected from each stratum. If the items selected from each stratum is based on simple random sampling the entire procedure first stratification and the simple random sampling is known as stratified random sampling.