the population is divided into strata and a random sample is taken from each stratum
properly related in size or degree or other measurable characteristics; usually followed by `to'
having a constant ratio
one of the quantities in a mathematical proportion
a small part of something intended as representative of the whole
items selected at random from a population and used to test hypotheses about the population
take a sample of
all or part of a natural object that is collected and preserved as an example of its class