For a national immunisation coverage survey, a team first randomly selects 20 districts from all districts, then randomly selects 3 wards within each chosen district, and finally randomly selects 40 households within each ward. This design is best described as:

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

Explanation

Sampling proceeds through successive hierarchical stages, districts, then wards, then households, with random selection at each stage, which defines multistage random sampling. Simple cluster sampling selects groups once and studies all units inside them, without further subsampling stages. Stratified sampling divides the population into homogeneous strata and samples from every stratum, while systematic sampling picks every kth unit from a list, none of which matches this staged design.

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

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