stratified sample
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 @[email protected] than that which might otherwise be obtained by random sampling.
PAC, 1990, 62, 1193. (Nomenclature for sampling in analytical chemistry (Recommendations 1990)) on page 1203 [Terms] [Paper]