6.4.2—Sampling methods

Simple random, systematic, stratified, quota and cluster samples select units differently. Stratification preserves subgroup representation; cluster sampling selects groups and may increase dependence.

Match the method to the population list and objective, and state how units are chosen. Convenience or voluntary-response samples often under-represent reluctant groups.

To estimate a school’s results across year groups, stratify by year and sample within each stratum rather than sampling only one class.

Random selection within a biased sampling frame cannot represent people missing from the frame.