To estimate immunisation coverage in a large state, a researcher first randomly selects 5 districts, then randomly selects 10 primary health centres within each selected district, then randomly selects villages within each centre, and finally surveys all children in sampled villages. This design is called:

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

Explanation

Multistage sampling involves successive random selection at several hierarchical levels, here district, health centre, village, and household. Unlike stratified sampling, there is no requirement that every stratum contributes to the sample; entire strata are excluded at each stage. Cluster sampling surveys complete groups at a single stage, whereas this design nests multiple stages of random selection, which suits geographically dispersed populations where a full sampling frame is impractical.

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

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