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. 2020 Nov 17;6(4):e21688. doi: 10.2196/21688

Table 3.

Sampling methods used for surveys in SNUsa with at least 3 data points for any KPb (Nc=68).

Sampling methods KPs


SWsd (Ne=416) MSMf (Ne=280) People who inject drugs (Ne=249) Transwomen (Ne=57)

Nonprobability sampling, n (%)


Cluster 34 (8.2) 10 (3.6) 17 (6.8) 5 (8.8)


Convenience 32 (7.7) 18 (6.4) 10 (4.0) 2 (3.5)


Facility-based 15 (3.6) 13 (4.6) 15 (6.0) 6 (10.5)


Snowball 62 (14.9) 99 (35.4) 74 (29.7) 13 (22.8)


Other nonprobability sampling 3 (0.7) 11 (3.9) 8 (3.2) 0 (0)

Probability sampling, n (%)


Proportionate to population size 12 (2.9) 5 (1.8) 3 (1.2) 2 (3.5)


Respondent-driven sampling 9 (2.2) 4 (1.4) 4 (1.6) 3 (5.3)


Systematic, simple random, or stratified 41 (9.9) 14 (5.0) 12 (4.8) 7 (12.3)


Time-location sampling 14 (3.4) 7 (2.5) 7 (2.8) 2 (3.5)

Unknown, n (%) 194 (46.6) 99 (35.4) 99 (39.8) 17 (29.8)

aSNU: Subnational unit.

bKP: key population.

cTotal number of countries.

dSWs: sex workers.

eTotal number of SNUs with at least 3 data points.

fMSM: men who have sex with men.