To estimate immunization coverage in a large state, investigators first randomly select districts, then randomly select blocks within each chosen district, then villages within each block, and finally households within each village. This sampling method is called:

• A Stratified random sampling
• B Multistage random sampling ✓
• C Systematic random sampling
• D Simple random sampling

Explanation

Multistage sampling proceeds through successively smaller sampling units selected in stages, here district, then block, then village, then household. In stratified sampling the population is first divided into homogeneous strata and sampled from every stratum, whereas here entire districts outside the sample contribute nothing, which distinguishes the two. Systematic sampling picks units at a fixed interval from a list, and simple random sampling selects units directly in one step.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

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