The subpopulation of the population studied is a subset of the population selected in the specified population, which is a new population (stratified random sampling). The purpose of dividing the studied population into strata, that is, stratification, is to isolate in a diverse population the possible homogeneous groups of individuals, e.g. in the opinion poll strata, are defined as occupational groups

• Sample allocation
• Stratifying variables
• Stratified sampling

• Stratification