Statistics.
a random sample of a population in which the population is first divided into distinct subpopulations, or strata, and random samples are then taken separately from each stratum.
Statistics.
a random sample of a population in which the population is first divided into distinct subpopulations, or strata, and random samples are then taken separately from each stratum.
Random House Webster's Unabridged English dictionary. Полный английский словарь Вебстер - Random House . 2012