Role of staratification in sample survey

The precision of an estimate of the population mean or total, besides sample size depends on the variability among the units of the population. To increase the precision of the estimate, we could divide the population into number of groups (called strata) such that variability within the group is minimum and maximum between the groups. In this paper, we examine the role of stratification in sample surveys and illustrate through a numerical illustration as to how stratification reduces the sampling variance which is the main objectives of a good sampling technique.