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Table 1 Comparative strengths and weaknesses of three sampling approaches [18]

From: Fake anti-malarials: start with the facts

Sampling approach Strengths Limitations
Convenience Rapid Low cost Sampling depends on collectors choice of outlet (risk of bias) Poor documentation—findings hard to replicate Prevalence estimates are not reliable
Random Sampling frame is defined to obtain representative sample from all types of outlets and/or brands Results can be replicated Need to authenticate and update sampling frame increases time and cost of survey
Mystery clients Outlets are unaware of survey so less chance of sample bias Information on sources of poor quality drugs limited to brand, batch and country of manufacture as stated on packaging
Overt Additional information is collected at minimal additional cost to mystery approach as provider is aware of the aims of the study Risk of sampling bias in samples collected, if some outlets refuse to sell or samples are deliberately withheld as poor quality is known by the seller