A sample consisting of portions obtained from identified subparts (strata) of the
parent population. Within each stratum, the samples are taken randomly. The objective
of taking stratified samples is to obtain a more
representative sample than that which might otherwise be obtained by random sampling.
Source:
PAC, 1990, 62, 1193
(Nomenclature for sampling in analytical chemistry (Recommendations 1990))
on page 1203