Uniform Allocation The simplest allocation strategy is to select the same number of samples from each stratum, which is an ideal approach if there is no information available about variability of units within strata, the cost of sampling is similar for all strata, and strata are of similar size.
Allocation Proportional to Size or Variation The number of sample units to select from each stratum can be made proportional to the number of sample units (or size) within each stratum. Variation in a stratum often increases with a the size of a stratum, so in some cases this approach can be considered as a rough approach for allocating more effort to strata that are likely to be more variable strata. To allocation proportional to stratum size: