a set of samples taken from separate subpopulations (even if they do not comprise the whole population) and it is valid to pool the results to generate statistics for the union of these subpopulations provided there is no overlap
Sampling scheme in which random samples are allocated to relatively uniform subunits within a population
A grouping achieved by dividing the population to be surveyed into a number of nonoverlapping classes or categories which together include all cases, followed by taking cases at random from within the categories.
A sample consisting of random samples from each subpopulation (or stratum) in a population. It is used so that the investigator can be sure that each subpopulation is appropriately represented in the sample.
