Stratified sampling involves dividing the population into strata based on relevant characteristics such as age, gender or region, and then selecting samples from each stratum, usually by random methods. This approach ensures that key subgroups are adequately represented in the sample. It can increase precision and allow for subgroup comparisons. Hence, the technique described in the stem is correctly termed stratified sampling.
Option A:
Cluster sampling selects intact groups such as schools or villages as the initial units and then studies all or some members within them; it does not primarily aim at forming homogeneous strata for representation. Therefore, cluster is not the correct completion.
Option B:
Option B, stratified sampling, focuses on homogeneity within strata and heterogeneity between them in relation to the variable of interest. By drawing from every stratum, it guards against underrepresentation of smaller but important groups, which matches the description in the question.
Option C:
Systematic sampling chooses every kth unit from a list after a random start and does not inherently ensure representation of specific homogeneous subgroups. Thus, it is not the best answer here.
Option D:
Quota sampling is a non-probability method where quotas for categories are filled using convenience selection, so it lacks the random component that defines stratified probability sampling. It therefore does not fit the stem.
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