In a community survey using cluster sampling, one cluster has 500 households and another has 50 households, yet each is selected with equal probability. This represents a problem of:

• A Systematic sampling error
• B Intracluster correlation coefficient being zero
• C Stratified sampling inefficiency
• D Selection bias due to unequal cluster sizes ✓

Explanation

When clusters of unequal size are selected with equal probability in cluster sampling, households in smaller clusters have disproportionately higher selection probability than those in larger clusters, introducing selection bias. The solution is probability proportional to size (PPS) sampling, where larger clusters have higher selection probability. This ensures each individual has an equal chance of selection.

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

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