It relies on the fact that the numer of sampled units from each stratum is directly proportional to the size of that stratum and to the standard deviation of the examined feature in that stratum. For a constant sample size, Neyman allocations provides the smallest sampling error. When the unit cost of the survey depends on the stratum, in the optimal stratified sampling scheme the number of sampled units is inversely proportional to the square root of the unit cost of the survey in stratum.

• Sample allocation
• Stratified sampling