Stratification & Sample Allocation
is the process of regrouping similar PSUs into sub-groups (strata).
Effects: better precision, flexible design, small sub-population coverage (or over sampling).
How to do stratification? (region) X (residence type)
Sample allocation: proportional, power allocation, equal size allocation (if budget is too tight).
: sort the sampling frame according to certain characters such as regions, urban-rural residence, sub-regions, districts, etc.., then select a pps sample.
There is no unique rule for stratification, it depends on country situation