An investigator studying injecting drug users recruits initial participants through a needle-exchange clinic and asks each of them to refer other members of their network who share the behaviour. This sampling method is termed:

• A Convenience sampling
• B Snowball sampling ✓
• C Quota sampling
• D Judgemental sampling

Explanation

Snowball sampling is a chain-referral technique in which initial contacts recruit further subjects from their own networks. It is designed for hard-to-reach or hidden populations such as injecting drug users, commercial sex workers, and homeless persons, where no sampling frame exists. Convenience sampling takes whoever is easily available without referral chains, quota sampling fixes predetermined numbers per subgroup, and judgemental sampling relies purely on the investigator's choice of representative subjects.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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