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The term sampling survey is used in conjunction with the sample of populations, eg collections of people, households, ect. Let the population of N units is divided into subpopulation of N 1, N 2,..., Nl units. These subpopulations are nonoverlapping and N 1+...+ Nl= N. The subpopulations are called strata. Stratified random sampling is a common technique when the variance between the strata is high. We use the following notation for stratified random sampling: L–number of strata; n k–number of sampling units selected from stratum k; n–total number of sampling units, n= n 1+...+ n L;