Multiple Lipomas Removal

Strata Stratified Sampling: Stratified Random Sampling

is given the name of affixation to sample size allocation between the different strata. Setting up different ways to spread the sample, among which four specialties:

• Uniform allocation: are taken every same, ie, are assigned the same number of units within each stratum This affixation favors the younger strata and large hurts:

• Proportional : In this case is proportional to the size of the stratum

with

.

All units have the same chance of being selected

• Allocation minimum variance or Neyman: In this type of affixation are chosen a way that minimizes the variance for a fixed . The problem is to minimize subject to . Therefore, the sample is divided as

.

• Optimal Allocation: Here is chosen so as to minimize the variance for a fixed cost . This cost is given by where is the cost per unit in stratum and is the initial cost. The allocation is:
  

.