Disproportionate stratified sampling

Stratified sample in which the individual strata or subsets are sampled in relation to both their size and their variability; strata exhibiting more variability are sampled more than proportionately to their relative size, while those that are very homogenous are sampled less than proportionately. This requires that some estimate of the relative variation, or standard deviation of the distribution of the characteristic of interest, within strata be known.