To estimate HIV prevalence among injecting drug users, a researcher recruits an initial group of index participants who then refer other members of their network, continuing in successive waves. This sampling technique is:

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

Explanation

Snowball sampling relies on initial contacts referring further eligible subjects through their social networks, making it the practical method for hidden or hard-to-reach populations such as injecting drug users and commercial sex workers. Convenience sampling takes whoever is easily available without any referral chain, and quota sampling fixes numbers per subgroup, neither of which matches the referral mechanism described.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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