Stratified sample in which the number of observations in the total sample is allocated among the
strata in proportion to the relative number of elements in each stratum in the population. A stratum containing one fifth of all the population elements would account for one fifth of the total sample observations and so on. One advantage of the proportionate allocation is that the researcher needs to know only the relative sizes of each stratum in order to determine the number of sample observations to select from each stratum with a given sample size.
